Won't marry me

Hannah • 20, young mommy to Marlinda and Clarissa, but super happy. Engaged 2-16-17

Honestly this is probably all my fault but it's still breaking my heart. Long post so bear with me. My fiance/boyfriend and I have been engaged for 7 months and together for 14 months. We have a beautiful 5 month old daughter and i raise his 3 boys as my own. Due to some problems between us (him cheating and wanting us to be polyamorous, his yelling, and several other things) I left him and was going to break up with him but ended up coming back. Now he refuses to marry me. He told me it's because he doesn't want it to end in divorce which I understand that. But he's making it sound like he never wants to marry. Like no hope for the future or anything. I don't know if I should stay because I do love him but I don't want to never get married. I'm just really torn. I also would rather avoid all the custody mess with our daughter