Like the other commenter said, unfortunately psychology and psychiatry is in a state where it's hard to get good objective criteria for diagnosing any mental illness; it's mainly reliant on self-reported data/surveys or observations of behavior. I think this is a big driver of the replication crisis in psychology.
I don't know you well enough to give a decent hypothesis, so I'm just going to guess and babble a bit: Generalizing adhd/executive function as being composed of attention, self-regulation, and motivation. My first thought is that rejection sensitivity could be emotional regulation thing, which might have some interplay with general self-regulation. My followup thought is something along the lines of rejection sensitivity involving paying too much attention to the negative and not enough to the positive. Re: maintaining friendships, I don't have enough information. Personally sometimes I struggle with motivating myself to reach out, make plans, etc. Other times I feel bad because I feel like I have trouble focusing on what my friend is saying or asking them to repeat themselves or otherwise being a bad listener in the moment.
Self-regulation is something improvable without medication, I think meditation is pretty effective. And Self-regulation can play a big part in helping manage attention and motivation issues.
Some of this might resonate, some of it might not. If you'd like support tackling your struggles, you can contact me at me @ my website name (but a good therapist might do a better job xP)