Don't know what to do

There's this guy that I've known since his mother messaged me outta nowhere telling me that she wanted me to be with her son because I had a good reputation, I was 15 at the time and I just went with it, I never met her or her son but I talk to him via Facebook, we've been talking to each other for three years now on and off, so I went to high school and saw this other guy, I really liked him and a few days later I found out that he liked me too so I started talking to him more, he asked me out on a date then asked me out the next day so I became fond of him, we're engaged now with a son and I'm pregnant but this other guy...I started talking to him again and turns out my feelings are still there, I imagine myself running off with him and going to his home town but everything else is stopping me, I'm not happy with my current relationship so he makes me happy, I can't be with him because I'm scared that I might lose everyone so right now I'm planning a secret trip to him, I told my fiancé about how I felt about him and how he's been unfaithful lately, I want to run away with this guy so bad but my mom might be disappointed in me, his mother doesn't like me anymore, his baby momma is probably psycho, and my son and unborn child, I'm in love with this other guy I haven't met but I still love my fiancé and I don't want to hurt him, I know what I'm doing is bad but I can't seem to stop, Everytime I try he'll just come back into my mind and I can't resist.