I used to have a similar problem, didnt know when to say no, let everyone ask for favors and i had a hard time putting myself first. And the worst part, it didnt seem they acknowledged or appreciated the time and effort i was giving them. Would they even say thank you? I think that pissed me off the most. You seem almost there in regards to the solution but you are missing the last step.

Simple answer? Learn to be ok with people being upset at you. Consider not pleasing everyone or anyone as normal. I know you like to help others, it makes you feel good and you want to be a good person.

But Fuck it, everyone is going to put themselves first, and its time you did so as well.

If they call, let it go to voicemail. When you have a bunch of voicemails. . screen them and DONT call the annoying ones back. Delete them. Avoiding even responding is best for you, so do it. Is it impolite? So fucking what? they dont respect your time, so they dont deserve a call back.

Establish new boundaries for your time, personal space, and life. And enforce them to the death. GF and parents I would say you have to help out, but they can also go overboard. Either way, as you mention cutting out your shitty friends who thought you were their taxi. . thats ok.

I gotta ask, did you go out of your way to be the friendly, always helpful guy? I imagine that has stopped now but if that was the first impression. . its going to be hard to fix. Also, learn to say no even if you could help, because you just dont want to. Even if you could give a ride or had the time to help, intentionally delay or refuse to help, just because. That might be the hardest but its well worth it. Really helps you better put such situations into perspective.