Why does my ex gf treat me like a stranger?

Because you have hurt her too much or maybe she wants you to stop playing around and ask her for forgiveness and get serious about her and you should get serious about it by the way, don't forget you got a child with her.

You are no longer a couple. Get on with your life and focus your attention to your child. Pull up your skirt and grow a pair. the child comes FIRST.

if you guys are young then that's the reason why she wants something different but it depends how it actually ended did u end it or did she? was there problems? was she unhappy? are you boring? those things comes to question.. you can be the best father and etc but you need to move on it hurts to see your x to be with someone else but trust me we men have to find someone else... and when she see you with another you see if she be mad or be like ok he moved on...

maybe she does not realise the good that she has, maybe she wants to taste somebody else,but this may disappoint her and she may come right back to you, or maybe she does not love you anymore. there are plenty fish in the sea, must have one of them for you, try somebody else ,you may be surprised she may come begging back but, then it might be too late because you may enjoy someone else.

Well it's obvious isn't it? She treats you like a stranger because...you're strange.

Why not concentrate in being the best father you can be? That really should be your priority.

that's how women move on - they let go of the past