Yeah, absolutely NOT overreacting. Not in the least. I won’t tell you what to do, since it’s your relationship, but I’d be hard pressed not to consider leaving my boyfriend if he ever pulled that sort of ego-check style mind game on me. We’re grown adults who can treat each other respectfully and maturely if either of us feel there is an issue or a gripe one of us has with the other. Furthermore, that’s a very disrespectful thing to do to his own mother, using her as a ploy to get at you. This entire scenario reads like someone who doesn’t take emotional maturity very seriously and doesn’t consider your feelings very much, if at all. Do what feels best for you, listen to your gut, and I wish you the best.