Do i tell him at all?

yess tell him he needs to know and is not a stupid mistake he was part of it,,, and dont have an abortion is really bad for your body and 99 of the cases regret having one.. he needs to be responsible for his actions and obviously his gf is not that importnat to him because he slept with you -__- so **** him and tell him and if he doesnt beilive you show him the pregnancy test