So to keep it short, since about April I have been involved with a married man. He is 37, and I am 25. I too, am involved in a long term relationship so I guess we both could relate on some of the issues that we have been dealing with in the both of our relationships, which in turn sort of started the whole affair.
We both agreed to trying our best at not developing feelings, which was totally cool at first. But lately I’ve been having strong feelings. I feel a lot of guilt on so many levels, and I feel so worthless ever since we started sleeping together. Each time we have sex and he leaves, I can’t help but due to the shame that I feel. It’s like he takes a piece of me each and every single time he leaves after we are done.
I really want to break this off, especially knowing that our relationship will never be anything more than what it is. But sadly I have fallen for him. I have nobody to vent to, and it’s eating me up inside. I’m just curious as to how do I let this guy go? How do I emotionally and spiritually pick myself back up again? How do I get my self worth back again? He took it all from me.
LemonVibe 
How did you get together in the first place? Cut off that channel. That’s easier said than done of course, but do it. This may require changing jobs or locations.
Have a face to face meeting at a public place and break up. He doesn’t really need much of a explanation. He already knows this is wrong and hurting all parties involved.
It’s time to break up with your other relationship as well if you aren’t going to work on it. Don’t follow a dead end relationship and stop wasting their time finding a partner more suited to them. Nobody looks back on their life and says “man, I wish I had spent more time with that guy I wasn’t in love with.”
Then work on forgiving yourself and healing. Take some time off dating just to be you. You need time to work through this and understand you are human. If you need to look for a licensed therapist to help you not cheat again in the next relationship. They could help you understand why you felt the need and how to avoid the issue in the future.