If you are more concerned about how you'd cope financially

[JeremyIronsWhileBenFolds]

than with how you'd cope without your DP when considering a split does it mean it's definitely over?

Just that really. There's a lot of back story but the bottom line is I don't fancy my DP anymore. Sex (or the absence of) is a big problem. Our life together is comfy and familiar and boring. It's like that line from Before Sunset "Cut to the present tense and it feels like I'm running a small nursery with someone who I used to date."

He's mostly a great partner and 100% a great dad and provider. He's my best friend. We've been together for 15 years and have two DC. I don't want to break up my family but I feel desperately unfulfilled and like there must be more to life. I know that if we did split we would be amicable and co-parent successfully. We are able to talk about the issues in an open and candid way without any fights or drama.

I've found that when I contemplate a day to day life without him I don't feel happy but I don't feel distraught either. I mainly worry about my DC, telling our families and how we would cope financially having to run two houses etc. I feel awful and selfish for even acknowledging these feelings but they're eating away at me. My parents have spent the last 40 years in a miserable marriage out of a misguided idea that it was best for me and my siblings. I guess I'm terrified of ending up like them.

Don't lose sight of the good things you have - all the stuff you listed is really important in having a happy, fulfilling life. I think you need to be really sure the love is gone before you act. Underneath that boring familiarity is the security of someone who knows everything about you and loves you completely.
I'm not saying stay in an unhappy marriage if you are really unhappy. But as a parent, you aren't really likely to be leading a thrilling life for a while. So maybe alone you would still feel bored, unfulfilled, just skint and lonely too!
Is counselling an option?

I'm not sure it means it's definitely over. It's definitely time to talk honestly about the state of your lives - assuming you've not done that already - and work out if the dissatisfaction is the cause of your relationship problems or symptomatic of something else. For all you know, he could be feeling as hacked off as you are.

I don't think it's as simple as that tbh

I don't want to undermine how you feel so I'm treading very carefully as I type this but you might think that you're more concerned about the finances because you're someone who deals in practicalities. Hence trying to work out financial solutions is a more pressing concern that considering any emotional impact. Sometimes it's easier to predict practical challenges than emotional upsets. Or, of course, you might be right and the biggest difficulty for you will be managing the finances. It's impossible for a stranger on the internet to know.

You sound as though you're carrying baggage related to your DP's miserable marriage. It might be worth having some counselling with Relate to help you come to terms with your DP's marriage and to tease out whether you're ready to call time on your own marriage too.

There's no energy or enthusiasm in your post. If that's because of your relationship then it doesn't bode well for its future,but if there are other issues pulling you down then talking to a counsellor might help with those too.

Thanks both.

We've talked at length about it all Cogito. We love each other, he fancies me, I don't fancy him. There are trust issues on both sides. I think he does feel frustrated and down but is probably angry at me because it's my "fault".

I wish there was some concrete way of knowing whether you were just having a rough patch or you had reached the end of the road.

I have been far too dependent on him over the years and it's all got a bit claustrophobic. I've made steps to change that by applying (and being accepted) on a course starting September. I want my own career and to not be financially dependent on him.

I just feel far too young to give up on having a brilliant sex life for the rest of my days. Then I read that back and think I sound like a spoilt madam.

Trust issues?

APlace you're right.

I am a pragmatic person. Too pragmatic probably. Sometimes I worry I'm a sociopath.

I am passionate about my kids and my potential future career (I am fanatical about the subject matter). I just don't feel passionate about DP. I even imagined him having sex with someone else and the physical act didn't really bother me (him ever having a DP that my kids would have to meet/be involved with or having more kids with someone else would be different and very challenging).

I am so inside my own head (up my own arse?) I don't know what I think or feel anymore. My brain is a permanent washing machine cycle of the same stuff.

My brain is a permanent washing machine cycle of the same stuff.
That's why seeing a counsellor on your own might help. It sounds as though you've been stagnating and now you can see a better future with your course (congrats on being accepted for it!). Going from being in a claustrophobic relationship to having your own interests and social circle will change the dynamic of your relationship but it doesn't need to end it unless you want it to.

Something you said struck me:
I even imagined him having sex with someone else and the physical act didn't really bother me
I used to spend a lot of time in my head, imagining different scenarios about different events in my life. I think I somehow thought that imagining bad situations before they happened would help me deal with them. It didn't. Now, of course, I'm not you but you sound as though you could be hiding in your detachment - approaching your relationship through practicalities and imaginary endings. You need to engage with the reality of it. Although, perhaps you're not doing that because the reality is so lacking for you. Could you have some time away from each other to see if that helps to clarify your feelings?