Why can we make it work as friends but not in a relationship??
As friends, he doesn't have to commit, he can do as he pleases, which translates to party, drink, stay out all night, repeat.
You obviously want more out of this situation than he can currently offer. Are you kidding yourself? Yes, i believe you are.
It's really not that complicated, he has shown you who he is, and you are choosing not to believe him.
Think about it, your living with his parents, usually when adults are in mature relationships they provide their own roof over their own head. As a parent of adult children, I cannot think of a reason that I would allow my unmarried adult kids to set up playing house under my roof, and here is why, if they haven't made the commitment to marry, they certainly cannot be serious, they just want a place to shack up, ummm, NO!
Not trying to be rude or insensitive, but may I ask why YOU are still living under his parents roof, if you are not a couple any longer? IMHO, you are just postponing ripping off that band-aid, as we all know that hurts a bit.