why is it that after snow was forced to lie and give james the impression that she doesnt love him, he still went after her?

I believe that when he first left the castle he was just trying to get out of marrying Abigail. He wasnt going after Snow. Then after he reunited Abigail with Frederick he realized that "true love isnt easy, but it must be fought for, because once you find it it can never be replaced." Snow is his true love, and he feels that in his gut. Then Red tells him that Snow does love him, so he had to find her.