Boyfriend has a child. How to deal?

Kayla
I've been seeing my boyfriend for 5 months now. He told me he had a daughter on our second date and it honestly didn't bother me. The deeper we get into or relationship the more I'm falling for him. It makes me sad to think that he's already shared that experience with another woman. I'll just have to accept that it'll be him, me and his ex involved in his life. He's a great dad and takes on all the responsibility that comes with having a child, but the relationship he had with his ex wasnt healthy and she breaks him down. It's tough to deal with her saying things to hurt him and him believing them. It's almost like the things I do to try build him up don't matter. That makes me feel like I don't matter because he has so much going on in his life. 
How do I deal?? Have any of you dated men with children?