How can i steal him?

this guy..ive known for a while..since my sopre yr..im now a sr..well..he had a gf..i didnt know..we became fwb's...well..im prego..and i think i love him..i wanna steal him from her cuz she obviously cant take care of him or he wouldnt be coming to me...and i know he wants me..he told me today that he wants me..and that he misses what we had...and that he misses me..thing is..i have a bf..but i still wanna steal him back..i know he has a thing for me..i know he loves me too even tho he wont admit it...how can i do it???