Sex while engaged

Hi, I just joined this group because I need some advice. My fiancé and I had a child together at 16 (now 20). We both recently were saved and I am battling some inner turmoil. We have been having sex since we were 14. Now, I feel guilty engaging in it, but he doesn't. We have been together for almost 5 years, have an almost 3 year old together, are engaged, and live together because of tense households on his side. I want to continue, but am struggling. He doesn't see the issue with it because of all the commitment. We would be married right now if we could (we can't because of pell grants for college). I just need help! What do I do, what do I say???