Two,
My husband had a real he|| of a time with me when we first got together because I was carrying so much mistrust....from somebody else's actions!
Little things like the stuff you mention -- like not mentioning he got on a social networking site -- would send me into a tailspin. He could've gotten mad, and once or twice he did, but eventually we came to an agreement that I just needed a period of time to recover, and during that period he needed to be STUPIDLY honest with me, and I needed to give 200% to try to trust him.
So when he got a Facebook account, he told me, and when he ran into his ex-girlfriend at a work function, he told me, and when he drank too much while I was out of town, he told me.....even though he shouldn't have had to. He did it for me, to show me that he had nothing to hide.
Maybe you just need a Brutal Honesty period too. Would your BF be willing to go this extra mile, even though he "shouldn't have to" ? Does it bother you at all that his best friend is a woman? (and not you?)
Would you be able to not snoop for a while, just to prove to yourself that you're strong enough to survive anything that happens, and it ain't time to worry yet?
Have you read "Codependent No More" ? Good book there.