I was intimate with a man in exchange for a favor. It’s been a few months, and ever since then I cannot stop thinking about how disgusted I am with him, and myself with making a bad decision that I had full control of.
The whole time with him that night in my head I did not want to comply. I never found him attractive and looking at him now is just the worst. That night I was making excuses to stop. And now I mentally feel screwed up.
LemonVibe 
We all make mistakes and some are harder to deal with than others. All I can suggest is that you come at it from another point of view. Question why you made the decision you did rather than the result. Learn from it rather than beat yourself up or avoid it. It’s not easy but it will help you to come to terms with the bad decision, even though regret will still likely be there at least you will be able to get as much positive as you can from it.