What does it all mean???

[Lady Pi Phi]

Okay, so let me ask all of this...

A boy I have been "dating" on and off for 2 years came back from Cuba on sunday. So we have a nice chat about who his trip was and then out of the blue he makes the point of stating to me that even though he had plenty of opportunity to "fool around" with multipal girls while he was in Cuba he didn't. So I'm thinking, okay, thanks for sharing. I'm not sure why he told me this? It's not like we're together. He can be with whom ever he wants. So I ask him why he didn't fool around with anyone, and all he says was, "just 'cause".
Okay, so what does this mean? I didn't push it any further, but the way I interpreted this was that he had a real reason but he didn't want to tell ME what it was. I don't understand him. What do you guys think it means?