To not know how to leave my partner?

[Chocoramj]

I've been with my DP for nearly a decade, we've had ups and downs but I'm just so utterly miserable; not because he's an awful person but because I've fallen out of love and feel utterly trapped. It's so pathetic but I just can't find the courage to split, we have a child and share a mortgage etc so the logistics are on my mind but it's mainly just i can't bring myself to do it.

How do you do it?

This sounds so tough. If you're certain there's no going back, even with joint effort and even couples therapy, then you have to just make time to sit down alone without your child around and be honest.
Either be honest now, or waste more years and still have the same difficult conversation but years too late. It's not fair on either of you to drag this out. It will be hard, but life is far too short to waste it.
All the practical stuff will work itself out eventually. Good luck x

The best thing to do is make a plan, and then have a place to go before you do anything.
A plan is an idea; you haven't committed to anything by making a plan. Break it down into steps, how will you leave and where will you go. What will you take.
Where will you live, what will you live on.

www.citizensadvice.org.uk/scotland/family/relationship-problems-s/ending-a-relationship-when-you-re-living-together-s/

This is such good advice, a plan stops everything going around and around in your head. Even if you change parts of it, and you can, it still makes things better to have one.