Ok I am dating a man with 2 kids from 2 different women. His youngest child is from the girlfriend he was so so deeply in love with that he even tried to commit suicide. When he picks up his child I stay behind and cry because I can't handle the fact he has to still see his ex. Any advice

My advice is to lighten up.
He will need to see the mother about issues over there child. This is going to be happening for the rest of this child's life. There is nothing you can do about him being hurt when he sees her,he has to deal with that.
So just lay back and give him all your love and support.