My $$ goes on the YES vote. Unless its your birthday where you turn 25, 30, 40, 50 etc, there is no real reason to text a message saying "I can't talk because <name> is here" or whatever. Honestly, ask yourself (everyone) if you text/told/phoned someone that you couldn't talk because your other half was there, would it really be for the right reason? What could possibly need to be said in private that you couldn't openly discuss with your other half in your presence?

Anyway, I know most won't agree judging by previous posts. Sorry about that, but unless he's wacky about girlfriends cheating on him, I'd place my bet on it. Women, like men, can have weak moments (although I suspect us guys have a lower weakness threshold) and do the "wrong" thing. You can get worn down by the constant badgering and just give in.

Another option you may try without confrontation or other heartbreaking mind wringing is to try a P.I. An investigator can do a lot of work on your behalf. Go on with your life as normal. If she's cheating, you'll have evidence. If not, you get evidence for peace of mind.