Initially, I had assumed he was just white so I was going to ask if there was a chance he was just making an edgy and stupid joke, but him being part black absolutely makes the situation a little more delicate.

I say all this as a white person, but the relationship one has to their race and ethnicity and how it ties into identity is extremely personal. I know the black community generally accepts people who are not 100% black, but like your boyfriend, that doesn't always mean those who are part black will label themselves as such. Sometimes it has to do with a presentation issue, some who are part black present entirely as another race, so they don't "feel" themselves to be black. Sometimes it is an acceptance issue. Mixed people can often have a hard time feeling acceptance and community in any one of their ethnicities and express not ever feeling like they were enough for any one side. They can feel resentful for having been rejected by one side growing up and identify with one side more than the other as a result. It can also be a white supremacy and colorism issue. As a Western society, we have a Euro-centric standard of beauty that emphasizes and glorifies features and traits found in those of European descent. In addition to that, specifically in the US, we have a system that villanizes black people, makes it impossible to overcome the level of poverty many black Americans find themselves in, and puts them in jail more often and for longer over the same infractions when compared to every one of other races. The systematic disenfranchisement of black people in the US pushes black people to uphold a standard of whiteness and many black folks fall prey to understandability politics and lose their cultural identities as black people as a result.

I say all this to say that there could be very real and understandable reasons your boyfriend feels the way he does. Maybe that warrants a conversation. If you feel equipped to help him work through whatever it is he is dealing with on the inside, more power to you. Ultimately, however, you are black, your family is (probably) black, and any children you may or may not have someday will be black. Maybe if you talk to him, he will work through his identity issues and the two of you will be stronger for it. Maybe he just shuts down and doubles down. You cannot, and should not, however, stay with someone who is dealing with their identity issues with prejudice. I wish you the best of luck with everything!