Was he genuine when he said this?

Long story short I like this guy jake and we have had a thing for a few weeks now and I’m really starting to like him … He had a reputation of kinda being a player in the past so I’m taking it slow with him to see how things feal… Yesterday when he wanted to go further then kissing I told him we needed to take things slow and after awhile of him trying to convince me otherwise he said he respected my rules. And he didn’t want to break them

             What really caught me off guard was when we where in the middle of making out very passionately and he stopped and looked into my eyes and asked me to make him a promise ... And I said ok and he said 

“to never hurt me” and I said “I promise”

  What I don't understand is why would someone who is or was a player say that. He's told me a little about his past and he told me he got really heart broken awhile ago and sounds to me like ever sence then he became a player. One of his close friends who is also my close friend told me that he isn't so much anymore and he is looking for a relationship .... But as of now we are just a thing. And I won't go any further with him unless we are official

Quistion is why would he say something like that? Cause this whole time I’ve been scared of him hurting me ( because of being a player) Is he changing?