Aibu ? Am I the arsehole ?

So you have no physical or financial independence, truly. He is abusive and controlling, you have to speak to Woman's Aid.
Stop putting all of your money jointly and only put your fair share, keep the rest and buy yourself the clothes you need and want.
I'm afraid I couldn't live with this man, personally. Might be a boiling frog situation and the ways he controls you might have crept up slowly and became your new normal, but there is nothing normal in the situation you describe.
If you fear becoming a sole parent, realise that essentially, you already are.

To be fair to him, I doubt all these behaviours are new, but you went ahead and had 3 kids with him anyway.

Oh love, you’re in an abusive relationship. Do you have anyone you can talk to?

Why are you asking him? Be ready for him coming in from work, hand over the kids and go. You're entitled to a gym membership so just sign up for one, his health is not more important than yours. You don't even have to go to the gym, take yourself out for a walk for an hour or so every night.

He's controlling and it sounds like financially abusive

He is taking the P. Why are you letting him stop you doing this, you’re doing it for your health and well being. What kind of relationship is this when he controls what you do, and just does what he pleases. I’d be getting rid of him for good and work on yourself and your self esteem as you certainly deserve more than this.

The gym is the least of your problems here.

What a dick he is!

Your OP was innocuous, but your updates are downright sinister.
Yanbu and I think he is financially abusing you and you are in a coercive and controlling DV relationship.
You shouldn’t have to justify buying a pair of trousers while he has 2 gym memberships.
You shouldn’t be trapped in the house with the kids. It is unreal that every time you try to go out, he deliberately disappears so you cannot go.
The concert you booked, he has caused a palava over- I think he will find a way to stop you from going,
You want to take care of your health and exercise which the doctor even recommended and he laughs at you and then actively prevents you from taking care of yourself
He justifies this as “you wanted kids so deal with it”

Step 1- a new bank account in just your name and your pay goes in there.
Step 2- Call Women’s Aid

I would keep some of that money back and squirrel away a running away fund. Find a good hiding place, you can start with a small amount so he doesn’t notice.

since he won’t give you any other money for gym membership, I would start calorie counting at home and follow some of the workouts on YouTube, bearing in mind that I bet you aren’t all of those names you call yourself. You sound lovely so please don’t talk about yourself like that 🌹

He does loads of hobbies, goes to TWO different gyms, yet you can't buy yourself a pair of trousers. Please just read that back. He is abusing you, financially and emotionally.

Some gyms have creches so I would look at that first. Failing that, you could try YouTube fitness videos or see if a local gym hires running buggies (or buy one) and go running with your DC in the pram. I used to do that around a local park till my youngest was about 3 and it was amazing- he always fell asleep.

I think he’s afraid if you lose weight you’ll realise your worth and leave him, because he’s a wanker.

With every update he sounds like more of a monster. Set yourself free.

OP, did he want to have children? It sounds like he didn't, was he this selfish before you had children together? You went in to have 3 with him over the last 10 years. Do you have your own income? You mention not having left the house without your youngest...ever so I'm guessing you don't work? Are you happy in this marriage? Could you afford to leave....would he support you financially and have the kids every other weekend?

I took it that she doesn't work when she told us she'd never been out without her youngest.

I really hope you are listening op. He is abusive and controlling. You need to leave this awful man.

Find a two year old funded place for your two year old and put them into childcare. Use the free time to go to the gym or look for a job. Sorry if you have a job already, I know you said you have some money. He sounds really unpleasant.

Someone I follow on insta goes to David Lloyd gym and her son loves the childcare there….agree so much with everyone he is getting off on limiting and controlling your life ….AND having children with zero effort

I can't see what the point of him is, OP. Doesn't love you, doesn’t love your shared children, restricts your life and your money. I cannot think of a single thing you'd lose if you left him, but I can think of a lot you'd gain.

Coercive control is abuse and it's illegal.
He's a criminal and you need to leave him.
Do you want your kids growing up thinking this behaviour is normal and ok?
Standing up for yourself is all very well... until he thumps you or throws you down the stairs.

He might not of course, but it's a real risk with a man like this. And posters advocating you tell him to stuff it, are potentially putting you in a dangerous position.

Just leave. He won't change

Of course wanting your own time doesn't mean you don't want your kids OP. Personally, I believe that every single person needs time for themselves, but it sounds like you don't get any, other than when the kids are asleep, and even then you're not allowed to go out, because it would mean that your husband would have to care for them. This is WRONG on so many levels OP, can't you see that? I'm guessing by the title of your thread that you can't? As there is no way that YOU are the ARSEHOLE!!

Do you have any friends or family close by OP, or has he alienated them all?

Do you work? Or is he also happy to keep you at home so that you don't get any big ideas about leaving?

Other than the fact that HE IS ABUSING YOU, which you really NEED TO DO SOMETHING ABOUT, it is possible to lose weight and get fit, without going to the gym OP. Why do you feel you've gained weight? Do you snack because you're miserable, bored, etc?

Going out for a walk will help make you feel better, as well as burning some calories, and presumably there's nothing to stop you doing that, whether you are looking after one child or all three. What about gardening? If you have a garden, the warmer weather and light nights are fast approaching, get out and lose yourself in pottering in the garden, again, it burns calories, whilst giving you the boost of being out in nature and getting fresh air. Or, how about dancing? All the kids can do that with you, and even if you're not able to do much to start with, if you do it often enough you'll be surprised how you quickly you will gain energy and be able to dance for longer.

So, even if you don't feel you can tackle the abuse side of things yet, because he's drained you of your confidence, why not focus on losing weight, and getting fit, without the aid of the gym, and then, when you're feeling better about yourself, hopefully your confidence will grow, and you'll feel better about dumping this piece of crap that is doing his utmost to keep you down.

Surely he’s home by a certain time most evenings to put the kids to bed?

So just go to the gym once they’re in bed.

If he doesn’t let you then you’re in a controlling relationship and need to separate.

Jesus he's vile. You can only cover it with self-depricating humour for so long. The way you talk about yourself is very telling. You need to have the confidence to get rid of this man, and I know MN is notorious for encouraging divorce over anything but seriously, he is controlling you and is abusive. Saying things like 'you wanted kids deal with them' is flat out gaslighting. He also chose to have kids, he also has parental responsibility over them. He knows this but he seemingly has you right where he wants you and know you won't put up much of a fight. You wanting to have children doesn't mean you should be the only one looking after them. If he didnt want children to look after, he shouldn't of chose to have them.

Tell him youre going to the gym whichever days and times you want, and he can watch the kids. When he kicks off, tell him he also chose to have kids and therefore has a legal responsibility to look after them. If he kicks off further, tell him that you may as well leave him in that case since you're already a single mum anyway.

Do not stand for it OP. Do not try and downplay how controlling and abusive he is. If someone treated your child this way in a relationship, would you just laugh it off? I certainly wouldnt.

You say OH rather than husband so I’m guessing you’re not married. In which case he has all the benefits of a wife without any of the obligations. He sounds like a dickhead.

You know you don’t have to live like this, right? You can leave the selfish, controlling prick and live your life however you please.

Worst case scenario he never has the kids overnight and you’re in the same position re time but without living with a horrible, pointless man.