Boyfriend/ex boyfriend

So my boyfriend or ex boyfriend idk what we are he says we're together but at the same time really don't feel like we are anyways he's thinks we should file for shared custody of our 14month old daughter in case we don't stay together. My problem with all this is he has two other child and one on the way. His old son he gets visitation rights with and his other son he has no rights to as he didn't show up for any court dates. I don't like the whole idea of shared custody because he's the kind who doesn't like to stay home at all at goes home late and I don't want my daughter going threw that. Now people are telling me if I want custody of her I can get whatever custody order I want but I know if I don't do the whole shared custody he's gonna wanna fight it in court and he is a good father but would he win in court ? I don't tho k he will just because he lost rights to his youngest son. I just need some really good advice I don't wanna lose my daughter over him being selfish and stupid and not thinking what's best for her