Hey Stan,
Please don't feel bad for quitting your 0 A.D. posts. Health and a fulfilling life go first, and I'm sure that everyone here knows that you have thoroughly thought about it before making your decision. Your work, care, and constructive attitude have had without doubt a huge impact on the development of the game and its community, and have made 0. A.D what it is today: Objectively one of the greatest open source games in the world. It can even compete with the best commercial games in the market which is - given the fact that this is all made by volunteers - not a matter of course at all. Thinking about the huge part that you had in it, what you did is outstanding and you can be more than proud of it!
It is only natural that the colossal effort you put into 0 A.D. would at some point wear you down. So don't think about your retirement as a weakness but instead be amazed at how long you kept up.
It's also a wise decision to make a clean cut as it's easy to get sucked back into old habits and wrongfully getting the feeling that one was supposed to deliver.
Once you have established a healthy mental distance, feel free to drop in for some games or good company without any pressure!
I wish you all the best and am sure that you'll find your energy again to have an amazing future :)