Being honest without hurt feelings

I have a tendency to be brutally honest without considering the another person’s emotions until after I’ve said what I said.

I recently had a conversation with a guy that I’m rekindling things with, and the topic of our intimacy came up. (Side note: he has a bad habit of speaking about other females that he’s either “talked” to or hooked up with) so as he was doing this, I blurted out “well maybe that’s the reason why you can’t make me cum”. As I finished saying it, I did genuinely feel bad about how I said it. But, I didn’t/don’t really feel bad about saying what I said.

Although I’ve apologized, how can I turn this subject into a clear message that may get through to them?