I think that he basically spit in your face, tbh. I agree with Mara that your bpd may be affecting this by making your feelings more intense than other people's feelings would be but it doesn't negate the fact that "have a nice life" is kind of a write off statement no matter how you look at it. Idk if it's as bad as saying eff off but it is like "see ya" in a way that is kind of shutting the door to someone in the sense that you don't expect to see or hear from them again. I don't see how it can be taken any other way honestly.

ON top of that, he hasn't even spoken to you since. A true friend, that remains a friend especially after someone has taken care of you in your time of need would feel at the very least, obligated to say hi and keep in touch. At least to let the friend/cousin/related counterpart know how you're doing. It seems clear to me that he's taken advantage and now that he no longer has a need, doesn't want anything more from you. Another slap in the face.

Don't let it bring you down, you did a good thing and it will come back to you somehow. I agree with letting it go, but definitely notbecause he's your cousin. Blood means nothing IMO.