Can you really trust him?

Soo. May SO and I have been together for 9 years, LDR for the last 3 years. 
My problem is I think he doesn't trust himself around other chicks. I mean he doesn't go to parties if there are chicks involved, he goes when all of them are boys or one of his buddies bring their GFs. 
He told me that better stay away from temptation. I know I know, I should be thankful for that,
But how can you trust someone who doesn't trust himself??