My husband said he isn't happy

Cock.
he should be around to chat about things. Not drop a bomb and jog on.
The first year (or. Um. Maybe more 😬) when you have a baby is tough and when they don’t sleep it is near on impossible. You need to communicate and share the load, your life would have changed massively in the last 12 months but it does get back to normal, all be it a new normal. Hormones, sleep, routine are all up in the air and it takes time to settle. After this you are not being unreasonable but the starting point is talking.
If he isn’t there that stops that happening.

It's unfair of him to drop a bomb on you like that before he goes away for the weekend. Presumably he knows you're now going to have a miserable weekend worrying and feeling anxious while he's pissing it up with his mates?

Has he spent the whole year being unhappy and not raised it until now? Is he right that you've been unkind to each other? Have there been lots of rows?

If I were you, I'd try your best to keep busy and put it out of your mind until he's back and you can have a frank face to face talk. Don't try and text or message him as you'll probably only disappointed by his lack of response. I think it's really rotten that he's done this but it is what it is - there is nothing to be done until you can have a proper discussion. Do you have a friend you can invite over for a movie and a takeaway once you've got baby down? You'll be better with company and keeping busy. Sending you a big unmumsnetty hug 💐

So -
He is leaving for a fun-filled weekend minus children
He is unhappy in HIS marriage
YOU are at home with his child (possibly planned and wanted by him to be a mini-me) but
HE is unhappy and

YOU are asking what to do? Almost what to do for him to make his own life better?

From the outside, this is not your job to fix tbh. He's a grown up. Before you had a child you were probably equal - why did becoming a mother make you HIS mother?
I don't mean to sound harsh, but you grew a human and are keeping said baby human alive. He's unhappy? He can talk to you about how HE is going to fix it.
Stay strong.

So he decided to unburden that on young then go away and enjoy himself at the weekend with his mates. I’d be so upset with this. Sending you big hugs.
why not throw a curve ball next week and don’t pander to him. Tell him how disappointed you are in him and things need to change. Don’t go running, it’s what he wants.

I don’t have children OP but from what I’ve heard and read. it’s normal for marital/relationship satisfaction to dip after the birth of the first child. It’s important to keep communicating.

When he said you've been unkind to each other, what was he referring to?

Sorry but are you sure hes not seeing anyone else or planning too? Bit strange to say that as going out the door for a weekend away.

It's not an excuse to cheat. If he chooses to cheat then that's irrelevant as being honest about his feelings doesn't give him the freedom to do what he likes.

There is some serious man bashing going on here.

Yes his timing is lousy but at least he is being honest. @Lottie585 it's great you've been trying to be a better version of yourself but given how blindsided you seem by his announcement then is it possible you've been so focused on you that neglected the relationship a bit?

My ex did this. I was thinking marriage and kids then one day he just said he wasn't happy. I felt like an idiot and just didnt see it coming at all.

Perhaps his timing was deliberate so you both have some time to reflect before discussing it?

I’m furious for you! So utterly bored of all these pathetic man-children!

He’s setting himself up with a great excuse to cheat and (if it was me) I’d be very clear that I’m absolutely onto him because I would not be able to hold back.

You are better than this and you and your little one deserve so much more.

He’s decided just before a stag weekend away that he wants a break, so basically I want to be single for my weekend away and then when I get back we’ll discuss if we’ll give things another shot.
I think he may have someone in mind to spend this weekend with and he’s hedging his bets.
You deserve so much more than this. I’m angry for you.

I'm afraid I agree with pp: the timing isn't coincidental. He will be planning to behave like a single man on this stag do.

And if this has come totally out of the blue for you then there is a good chance he has already had his head turned.

It's absolutely awful for you but I think.you should use the time he is away living it up on this stag do with his pals to start thinking about how your future will look without him. Because he has now shown you his lack of commitment to you and his child.

He’s being very cruel and childish dropping this on you and then buggering off for the weekend.

Feels like he’s lining up an excuse.

Very cruel of him OP and I'm sorry you're going through this. Did he want a baby? So many men just go along with it because they don't want to look like monsters. And some men say they want kids but are floored by the reality. Be prepared for the fact that there might be an OW involved.

Sending you a hug - that first year with a new baby can be so hard, and you've done well by starting to tackle the OCD. Your husband is allowed to find ithard too, and I don't know if there's ever a good time for him to tell you that. He's not necessarily an arsehole for telling you it now, though it's not ideal. I don't think it will help your marriage to just get a chorus of "He's an arsehole". None of us is perfect. But tell us, do YOU ever get a weekend off, or a night off? Because if not, he's not doing his share.
I'd suggest you get into couples counselling ASAP. Don't take no for an answer, just tell him you're signing the pair of you up for a session - easy to do an online session so you don't even necessarily need a babysitter.

You need professional help with the OCD and also with finding a fair balance in this marriage. Maternal anxiety and related disorders aren't good for anyone involved, not you, not your baby or your marriage, so your mental health needs to be prioritised. Especially for your baby's sake; if you're happy and healthy then baby benefits.

Now he has the perfect excuse to cheat whilst hes away. What an arsehole

I'm really sorry but seems like he said it right then, before fucking off on a stag do on purpose. So when he cheats on you that will be his justification. I'm so sorry. A pp was right. Be pissed off, not sad😡

He could have strived to educate himself on becoming an excellent parent, learning about child development, enriching his knowledge about feminism and how to excel at being a husband.

Instead he announced he hates having a child and swans off on a drunken stag weekend.

Time to find your anger. It's justified.

While he's away swilling beer, take time to think if this man is worthy of you, if he enhances your life and if you want to stay married to him.

Yes, that would be my concern as well.

He’s an arsehole. He has said this to give himself permission to do whatever he wants this weekend. Or possibly has started something already.

Leaving you to worry all weekend, and possibly be so glad to have him return you will put up with any old crap going forward.

Honestly, he is showing you who he really is, please pay attention. Spend your weekend looking at how you could manage on your own. It’s scary, but much better than years of this shit. If he’s already moved on himself you’ll at least be better prepared for it.

Yes, I agree with pp that his timing is awful - cruel.

And I would not blame you if you messaged him and told him not to bother coming back unless it’s with an abject apology. I would also hope that if his parents are alive that they give him a massive bollocking, because if my DS did this he’d get one from me.

You need to think through what both of you could do to improve things - do you need more time alone? Dates? If so, sort out a babysitter. He needs to say what he is willing to do, not just complain about you.

But - you also need to be prepared for him to come back and say that it’s over.

We obviously don’t know what has gone on, but I’m struggling to find much sympathy for a bloke who doesn’t seem to find joy in his baby. Yes, the first year is usually challenging, but I can still remember how my DH looked at DS when he picked him up and played with him despite colic etc. I’m sad for you that he doesn’t seem to show this, just whine about how awful his life is.

At first I had some sympathy, sounds like you've both had a difficult year.

Then I read your update about how he did it as he was leaving for a stag weekend, and that's just cruel.

That's a proper shit thing to do to you OP, so not only has he thrown a grenade he's now off on a boys weekend drinking and who knows what. Whatever happens you need to be angry about this not sad, he can absolutely be unhappy and talk to you about it but to do it this way is a dick move