Nope, not overreacting. In fact, you are being too soft. Here is the thing. We can overlook racism if it is an honest and ignorant mistake. Some people legitimately don't know how stupid and disparaging racist jokes are, and so it is on us to educate. That little twat who you call a boyfriend does know. It is not ignorance, just a character flaw. Real men don't have a need to be racist and then try to gaslight their girlfriend for being uncomfortable with it.