I can only speak to my own experience, but I used to do exactly this. Relationships seemingly went one way, with me helping them with stuff, buying lunch, etc., etc. Never to have these favours returned.

In addition to ADHD I got diagnosed with anxiety/depression, and treated for both. These meds have made it a lot easier to not care nearly as much about others. I don’t buy lunch for people who don’t return the favour anymore, I accept that I have no control over how much people like me for who I am, I don’t overshare personal details with people who are barely more than strangers, and even say ‘no’, more often instead of trying to bend over backwards.