Unhappy and have very strong feelings for someone else.

[MoonshineWashingLine]

My dp and I have been together 5 and a half years. We have a 4 year old and my 8 year old from my previous relationship. Tbh I am only with dp because we have our daughter, we would not be together otherwise. I feel trapped. He is a great dad but not a great partner, for many reasons. I'm not attracted to him anymore and over the last year or so I've developed very strong feelings for a friend. Said friend is on my mind a lot. I feel like we have a special connection, we get on very well, have loads in common and I feel a strong urge to be with him. I have no idea if he feels the same way but he is also my partners friend so I'm worried about bringing it up. I don't think I should bring it up while I'm still in a relationship though tbh.
I feel lost and very down about the whole situation.
Does anyone have any words of wisdom?

Life's too short. You love someone else and not your DP anymore. Even if your friend doesn't feel the same about you, you know you have to leave your current relationship, don't you? If your DP is such a great dad, he'll be great at co-parenting without being in a relationship with you.

That's the problem, he will insist on joint custody (as my eldest has with her dad) but our 4 year old still needs me during the night and I worry about being taken to court for custody. We've almost split before a couple of times so we've discussed this previously. He made it clear he will make things very difficult for me if we split and I don't agree to joint custody.

Leave. Do that first, and for yourself. The rest will follow in one form or another.

He made it clear he will make things very difficult for me if we split and I don't agree to joint custody

I can see why he'd want joint custody but the threat to make things difficult for you is yet another argument in favour of leaving. How is a bitter custody battle in the best interest of his child? So, not such a great dad after all... Is there no compromise to be had regarding overnight stays until your DD is ready to let go of you in the night? She'll grow up soon enough and then joint custody might be an option?
He sounds very confrontational and you sound like you're the victim of emotional blackmail.

The joint custody surely isn't a bad thing? Why wouldn't you agree with joint custody? Because it sounds to me like he's trying to protect and maintain a relationship with his child, which I would do so fiercely if I was in a position that I'd barely see my child.

Also, how were you with your other child's father? He will have mental notes if you've been unamicable towards your other child's dad.

My eldest goes to her dad's half the week because she is very close to her dad and step siblings. It's a decision we only made last year and it was for her benefit, not mine. I honestly don't think our youngest would cope without me for long. She is very attached to me.

No issues with my eldest's dad either, we get on well now.

I wouldn't want him to barely see her either, I'd just want him to have her Friday evening till Sunday evening or something.

Don’t let the custody thing hold you break from ending an unhappy relationship.
You can’t really stop him trying for joint custody, he’s as much a parent as you. Honestly at 4 years old your child will be grand at night without you, her dad can comfort her.
Do you work? Does he?

@TwilightPeace we normally do both work but covid has buggered up our jobs. I'm furloughed indefinitely and on half pay and dp is trying to find himself new work as he's self employed. He does have a job to go back to in a couple of months though if all else fails.
I think the custody worries is partly my feelings as well, I'm not sure I could cope with not seeing both my girls for half the week. It's bad enough with one. I feel like a part time parent to her. I don't want loose my youngest for half the week as well