Almost 5 years ago we met online as chat friends. I was lonely and needed someone to talk to and he was going through a rough time with his wife. It all started innocently, I thought for some reason I could help him with his problems. I was wrong. He was looking for more than a chat friend. We met and became more than chat friends. I had never done anything like this before in my life. I know I am in love with him now and from time to time he emails me. He really uses me and plays with my emotions and I seem to allow it. I am tired of it now and want to let go. Please tell me how

I can only speak from my experience and others will probably disagree, but when you allow this to happen the best is be careful put yourself first, don't beat yourself up if you do something that you wished you hadn't (calling, contacting, etc) WE ALL DID AT ONE TIME OR ANOTHER.....
being happily single is an alternative. Even if society is beating it into your head that you MUST have a mate, take some time to heal before going back out there.

There are plenty of good people to love, Learn the lesson.

And the universe will take care of the rest.

If you have to --stay off the website and the chat that he is on.
Get a new email and stay off your old one if that is what it takes.
Tell him you don't feel there is anything you can do for him and you feel there is no future if you have to

Just cut off all contact and move on with your life.

Stop all contact, and start loving yourself enough, to stop accepting his selfish crap. Hard work, but you will be better off, in the long run.

I agree with the others here. Cut off contact. Change your email and if you want to chat, go to a different chat room where he won't contact you. Stop calling him, contacting him. If he contacts you, tell him that you don't feel it would work between you two and you don't feel the relationship is healthy for you. Then, if he contacts you after that, ignore him.

While you are trying to get over him, try to stay busy. Go out with friends, get involved in a new activity, volunteer, take a class, whatever keeps your mind off him. Those activities are a great way to meet guys too! I think the best bet is to be single for a little while, and give yourself time to get over him. You deserve a relationship that you feel happy and healthy in, and since this guy isn't making you feel that way, it's time to move on.

If you have to change your user name(s) on the internet do that too.
If he has your phone # change that too.