If I Left would I be wrong?!?!?

A Year and a half ago my son was born, then three months later i found out he wasnt mine. but i was already attached to my son so i staied. for a min his Bio-father was trying to come around but not for long. then me and my Baby Mamma (BM) broke up. but i was still there for my son. we still messed around tho. so when we finnally got back together we found out that she was pregnate. She told me that she was talkin to someone and it could be his.ok soo like a couple days later the chick i was talkin to said she think she could be pregnate. She took a pregnacy test and found out she wasn't. i went to my BM and told her That my ladie friend could be pregnate to see how she would respond. SHE FLIPPED. she said that that was who i needed to be with then and said that if the baby inside of her was not mine she was going to be with the other guy. then i told her that she isnt preg. and said i dont want nothing to do with her. but she cryed so i wouldnt leave her son. Would i be wrong.