1st step, you're not responsible for anyone else's feelings.
I have more than once had sex, or gone further than I was really comfortable going with men, for the sake of preserving their feelings, or because I felt I had already taken things too far to back out. Almost all of my female friends have a similar story. How do I convince myself that I don’t need to have sex with someone to protect their feelings? And how do I find the words to politely end a sexual encounter after I become uncomfortable?