My girlfriend wants to adopt my son?

I'm 17 and my girlfriend Molly wants to adopt my 4 month old son Joesph. He was conceived during a one night stand at a party in which i met his mom. We dated for awhile but broke up because i didn't love her and thought being together for the sake of our child was wrong to her and to myself. She was pissed she is in love with me and told me i would never see Joesph again and for 3 months i haven't. I miss him we are currently embroiled in a bitter custody battle i want joint custody. She is a great mother i just don't love her in a romantic way she is very important to me and i would do anything to protect her and Joseph. I love Joseph and miss him so much she lives in a different city and i drove their as much as i could and spend weekends just to be with my son. He means everything to me. I am in love with Molly and we plan on getting married in the future. She is rich and has been helping me pay child support. She wants to adopt him ui don't know. His mother is a great mother and i don't wanna take him away from her. Although one day Molly will be his step mom and he will be her stepson. What should i do?