I caught my boyfriend in bed with my 15 year old daughter?

I came home from a business trip on Monday at 6:30 in the morning. I go upstairs to my bedroom and my boyfriend wasn't there. I go to my daughter's room and my boyfriend was there asleep on top on the bed with an empty beer bottle and my daughter was asleep under the covers. I flipped the f*** out. They both woke up totally confused. I didn't even want an explanation, I just told him to leave before I kicked his a**. I threw his s*** out of the house and asked why my own child could do something and she said that she had no clue why he was in the room and that she was sleeping. He came over later and tried to explain the situation. He said, his friend came over last night and they were drinking. Friend left and he kept drinking and that he had no clue how he ended up in my daughter's room, but that he must have ped out on her bed and that nothing happened.I asked why he was drinking so much because he's usually doesn't and he said he had a long day. I've sat my daughter down countless times this week and said "Lillie, if Jack has ever made a p at you or if something has ever happened you need to tell me. I promise I won't get angry" and she says that nothing happened and that she was sleeping and that Jack has never hurt her. It all sounds plausible and everything (she's a VERY heavy sleeper) but I'm still unsure. He wants to move back in but I can't get that image out of my head. They weren't touching or anything but all my "mom signals" are going off. I don't think anything happened but still people do things when they're drunk that they secretly want to do when they're sober right? The thought that he's attracted to my baby is heartbreaking and disgusting. He's sorry and says it'll never happen again. We've been together for 1.5 year and I love him but something's not right here. I don't know what to do. Help?