You're not out of line at all! Goodness. Everything Hankster said.

I get what you're saying about the heads up. It would have been nice for you to be able to make the choice whether you'd be ready for that or not. His excuse is lame and doesn't make any sense. If he thought you wanted to meet her, all the more reason to tell you she'd be there. Or at least be the one to introduce you and make it at least a teeny bit less awkward and mind-gamey -- I mean even if you knew he had a live-in girlfriend, and it was open and on the table, it would still be weird of him to let you figure out it was her on your own rather than say, "Oh! Let me introduce my partner, X." In summary, he's at the very least guilty of being stupid and avoidant, and at worst, it is a little sadistic.

The loving glances: barf. That is not a pleasant surprise. I'm sorry you had to deal with that.

ETA: meant to say before that just because you know he lives with someone doesn't mean you also know she's in his meditation group! MAKES NO SENSE.