I say go with your gut and if she is hiding things from you then that means that she is doing something. My boyfriend did the exact same thing and it was so obvious.....would not let me stay near him when online .....took his cell phone upsatirs when a call came thru and he started coming home really late and then just stayed out all night...and then one day ....i caught him and the girl and believe me...it is not a good feeling at all and i am hurting so much over this...so very very much........this is the first guy that i ever slept with and he gave me his word that he would never cheat on me and now who feels like the stupid one?.....not him......ME.......and i am the one suffering and paying for it......and the unbelievable thing is he was the one accusing me of cheating and when i confronted him..his reasoning for it all was that he was bored but she did not mean anything to him.

Believe me.....you will be the one left to deal with the hurt all on your own and nobody will be there for you at all.