Most Helpful Guy
It is highly unlikely because that is not who he is right now in his life. People like that never change for any one woman. It requires real effort and time and usually some kind of personal experience that brings with it some kind of realization or epiphany into their life.
Most Helpful Girl
"I was the only girl he ever let sleep over in his bed with him"
^^ How are you so sure of this?
I mean, you said yrself he was "a real player". In other words... you can't be sure of this at all. You can't really be sure of, well, anything.
"Players" normally lie a lot, and fake lots of shit. Did he do these things?
If he has a history of lies -- even if it's a relatively short history -- then it's unwise to trust anything that develops, here.