>>6580418relatable story mate
it seems like people started over-stepping a few bounds with your selflessness. being the nice guy feels great until your whole life becomes being nothing but the nice guy. If you're able to do all these favours, I'm sure you're a jack of all trades and you'll be able to find great success in life.
Maybe try out volunteering at a children's hospital or something, where your helping-people attitude will truly be appreciated, especially by the patients. Or try out some gratifying hobbies that are easy to lose yourself in, like exercise or cooking. As an added bonus, all of these function as legitimate 'excuses' but rather reasons (putting yourself first) to refuse someone asking you for help.
Don't worry too much about having an identity crisis. Being you should come first, mate.
Good luck.
(nice pape by the way)