5 month old sleeping on stomach

My baby is 5 month going on 6 months on the 17th of April. He finally learned how to roll over a few days ago and now he won’t stop. He only know how to roll over from his back to his stomach but, doesn’t know how to roll from his stomach to his back. When it’s time for bed I put him down on his back and he instantly rolls over to his stomach. He can hold his head up but I guess he gets tired of holding it up and, he puts it down onto his bed that’s when I go and roll him back over to his back. I do this about four times until he falls asleep but he still rolls over to his stomach. I check on him every now and than to make sure he isn’t on his stomach but, one day his dad had put him to sleep and my baby had fell asleep on his stomach. His dad had told me that he was falling asleep on his stomach so he didn’t want to move him. His head was on one side where he was able to breathe. That night he fell asleep for such a long time and only woke up once when usually he wakes up 3-4 times. I still woke up every once and awhile to make sure he was breathing I was so scared and still am. We have tired sleeping him on his side but just ends up rolling to his stomach. At this point idk what to do. I sleep him on his stomach he seems to like it and sleeps for a long time but, I get scared he stops breathing. I sleep him on his back he ends up on his stomach waking himself up. He sleeps in his own crib even when his dad is away at work. Any suggestions