Bitter much?
He has no reason to know whether this "boyfriend" even exists. Or if she loves him, if he loves her, or if he's fucking someone on the side, or if she wants to get out of this relationship. He doesn't know, and when you are starting to get to know someone you can
never know. She might have entirely legit reasons to cheat on her boyfriend. Show me someone in their early 20's that will cleanly cut and end their first relationships fair and square before they move on to the next one! Sure, when people get older, know what they want and the consequences of their actions, but not in the beginnings.
Then some BS about controlling sexual urges more. This is not about urges, it's about him not being casual and confident enough, simply because he hasn't yet experienced that girls are just normal human beings and nothing special to raise an eyebrow about!
It's more likely he "controlled" his urges too much. Basically not being relaxed and clear about it.
and LOL:
Basnak and Loyalty. You don't want someone to be with you because they are fucking LOYAL
You want them to be with you because they like you and want to be with you.
Let me put out a general warning: If you try to control someone, it will backfire and they will only try to get away even more. 
Poll