First, don't feel like it's you that's ending this. You said yourself in your OP that he wasn't taking you seriously, you tried for years, and this is simply too late. He wasn't fair to you all those years you tried and he didn't.
I think you should sit down and talk to him again (get angry if you have to) and tell him he should have tried years ago and now it's just too late. That all this family stuff is just confusing the kids. It's not fair to them and it's not fair to you. That it doesn't matter how hard he tries, nothing will undo the years of him not trying, and of you trying in vain.
That his "trying" is him being selfish again. He didn't want you when he had you, and now he doesn't have you he wants you... but that it's not just about what he wants. You wanted a happy family years ago, now you just want to be happy and that happiness doesn't include being in a relationship with him as anything other than co-parents.
Tell him to stop focusing on trying to get you back and instead focus on trying to minimise the affect this will have on the kids. Tell him you won't be going over this again. No more things as a family. No more of him trying to guilt you.
Don't reply to his needy messages. Don't go on "family" things anymore.
You said you still care about him, you still respect him - it's hard to turn that off. He's still the father of your children. He's still the man you spent 8 years with. He may just need this closure. He may just need to talk it out again. You've come to this decision and in a way that makes it easier for you. He's still coming to terms with what he's lost. He's feeling guilty, he's freaking out. He may just need for you to tell him that you don't hate him, you just don't love him in that way anymore.