The attraction you feel for someone can fade if you let things get boring if you've been together for several years. You fall into a routine, it's why some people try and argue that monogamy isn't a natural biologically. You need to keep the attraction going. While going poly could be an option, I don't think experimenting with that until you discover it's for you is wise given you have a very young child.
From what you've explained so far, I don't see how being with a women is going to help, as surely the same thing will happen in a few years once you're with a women
I'm sure speaking the the commenter above will help too. Have you tried reaching out to a councillor who specialises with LGBTQ+? They should help you talk through you feelings to discuss if this is a relationship to stay in.
Again I'm bi, and this seems like grass is greener mentality. (I've dated women as well, trust me, men and and women can both come with equal problems in relationships.) Good luck!