Very often & it was great, but then you found out he cheated on you with his first love and started something with her.... So after you found out about her- you ended it with him, and she left him too... Well, since you're long distance, would you offer to just be his phone sex buddy because it was that good? But you know 100% you'll never trust him or date him again?

Because I really still want the phone sex, but I'll NEVER trust or want him again. Thank you for answering, we're both in our early 20's.

I wouldn't do it, only because of the risk of getting involved again despite thinking I wouldn't.
If you are sure you will not get upset or involved in an emotional capacity ad enjoy the phone sex then why not ?
Better yet, if you really love phone sex, go work for a service where you'll get paid? :D