I don't know if there is a rule of thumb, but I kept doing things that made ME happy, but didn't over indulge, and if there was ever a time that he ruined it with "Well I don't get you at all - you take my blah, blah, blah, but then? You turn around and take us all out to dinner at yak, yak, yak!" That was it. No more dinner at yak, yak, yak. He ruined it for me. It was like he was saying to me - I'd rather have what I want than what makes you happy. So that cut that out immediately, and Df and I would just go without him.
Eventually you will find a balance of what you can do with him that isn't over-indulging. The weird part for me was, by the time you find that? He's off on his own with his own life and you sit back and think "YOU BONE HEAD DUDE! I wanted US to do that!" and it tugs at your heart a little that they don't seem to want to do those things with you anymore - but like now? Two years later? Dude would and has said - "I'd give anything to have dinner with you tonight Mom - even if it was sketti on a paper plate." Which he used to complain about all the time. So eventually it does come full circle. You just don't give them the chance to find out what their wants are without having a few regrets.