The only proper response is to abstain from his "meat" from now on.

How do you secretly feed someone meat???

Dump his ass. That's so disrespectful to your beliefs.

OP I am so sorry. That is an incredibly immature, disrespectful, and asshole thing to do. Because you were ignorant of his behavior, I 100% think you can still consider yourself a vegetarian. What an absolute douche.

that's what you get

Sounds like your boyfriend needs to learn a bit more respect for you OP.

I'll admit, him doing that was wrong. However, to all those saying that it is wrong to kill animals for the meat, that is stupid. I know you could use just for their milk and etc. but killing animals for meat and furs was a necessary part of survival back in past eras, and there is nothing wrong with doing it today. In my opinion, as long as you don't make the race go extinct, keep population in check, do it humanely, and do everything you can with the animal's body, then there isn't anything wrong with it. (this is coming from someone who hunts there own meat most of the time)

Being vegetarian for whatever reason doesn't matter here. The fact that someone close to the OP was disrespectful of her decisions with her own body and that is the only real issue. It's like your spouse putting holes in your condoms or substituting mediation for tic tacs... I'd probably just dump his butt. He doesn't sound as if he can be retrained adequately to keep if he thinks that this kind of thing is funny.

tell him you think it's "funny" that he still calls himself your boyfriend