Originally Posted by Monster.
Honesty, this sounds like he is definitely doing something shady. The phone thing alone I might have passed because that sounds like it could happen. People get wrong numbers all the time, shit happens. But none the less it sounds sketchy. Combined with this girl on facebook something could be going on. However that could also be explained. She simply could have been defensive and wanted to hurt your feelings because you called her out on hitting on your boyfriend.
If he is consistently telling you nothing is going on and you have no really proof that he is doing anything wrong you should believe him.
Just be cautious, tell him how you feel about how your trust is being strained because of the issues. Make sure that he understands where you are coming from.
It really does sound strange, good luck. I had a boyfriend who did things like that once. I feet so much better with out having to be constantly unsure of his behavior.