Why can't I just let him go now?

Well, most of the time you are probably thinking about your child more than about what makes you happy. Now there are sacrifices that must be made for a child, but definitely not your happiness especially in the long run. As much as you are letting him go, in the sense that you do not see him as being Mr Right, you will never let him go since he will always be the father of your child. Stable relationship are important when considering a small child, should not be a rollercoaster of a ride. If staying with him was the only way to keep him in your child's life, then you deserve a lot better since he should love and care for his child, with or with out being with you. I am sure you have no regrets with trying to make things work, for you and for your child. Let him know that it's not a goodbye, since you are going to want him to be there to help you raise your child, as well as be a good father. You still need him, but not for yourself, only for your child. You never know how things might end up down the road, you might see a new light in him, and want to work things out.

Well first off, were/are you married to the man you had children with? Being a child of divorce/breakup it really changed me at a young age. Having two parents is very important for children. so you should try and make it work for your child

the reason why you can't let him go is because of your child and he has been there with you through that. But I know how you feel it takes time for you to let him go. My ex and I thought I was pregnant and he wanted to be there for our child if we were then when we found out that I wasnt he was so upset and even though we werent together we wanted to make things work even without a child but it took me 2 months to get over him and now I've found someone who I love dearly. But just give it a little time it might seem forever but its really not.

That's an answer that only you know.

Maybe you don't want to let him go because you feel safe with him?
Maybe you want him to stay around because of your child?

In the end, you have to decide what will make you happy in the long run.
You said yourself that you know the relationship won't work in the end.
so, will you be happier dragging it on?
.or ending it now?

This is something only you can decide.

Well, I think you don't wanna let him go because you want what is best for your kid, and no kid is happy to see their parents getting a divorce even when they are still young. Because once they get older it will be hard for them to understand what went wrong with the relationship. So don't leave him. Keep working it out, but sit down at hours at a time and talk about your disagreements or whatever it is you are fighting about. I hope my advice helped a little bit [=

You probably don't want to leave him because you two have a child together. I know you would want your child to have a father but it's just as important for a child to grow up in a healthy environment and in a loving family.