Sounds like a lot of pressure, I wish I could say this is going to get better but you know as well as I that it will not. I think it was very mature of the new fellow to cut off contact. The reality is you can not burn a candle at both ends......before long you will get burned.
Sex is a interesting factor in a relationship, while it is and never should be the main reason for the relationship it also has a very crucial place in the relationship and without it there is a bond that has never been fully formed. It is that bond, or connection that you are missing that has allowed the second relationship to occur.
In the end you have to sit down and figure out who and what you want. The last thing you want to do is make a huge mistake and choose one over the other while you are under so much stress.
What I would suggest is sitting down and thinking about a few things. The first being your current boyfriend. If you could fix the sexual issues would you leave the other man behind? If so then your current boyfriend deserves the chance to fix this. While he knows this is a issue.........it sounds like he has not come to grips that it is enough to end the relationship. If you are willing to stay with him if this changes then I would suggest sitting down and being honest with him. You need to tell him the truth about what has been going on and why. Let him know that you love him and want to be with him, but the sex issue is a breaking point for you. You need to tell him exactly what you want and need......make a list so you make sure you have all the key points. Ask him if he is really willing to work on it. If he is not then he has made this decision and thus you know it is time to leave. If after 10 years you are feeling this way.........it will not go away on its own. It will get worse with time. If you are wanting to make it work then you must be honest and let him know what the issues are. If you just can not tell him about the affair then be straight to the point........let him know what you need and that you do not feel comfortable getting married until you are sure that these issues are under control.
A big issue is putting off the wedding.....I know that seems like a big thing. But the last thing you need is to be pushed in one direction or the other based solely on the wedding approaching. Once that stress is removed you can concentrate on fixing the issues in your relationship. I would suggest a relationship counselor. The counselor can help you both understand the needs of the other and how that affects your relationship. If you feel he is making progress and you want to be with him then you can move forward with the wedding.
Now for the tough part.......if you just do not feel that a change is going to help then you need to be honest with him. Though do not make this a matter of choosing one man over the other....a year from now this new guy may not even be around. You need to make this decision for yourself. Are you willing to continue on without that connection? Or are you willing to try and get that connection back? If not then now is the time to end the game and be honest with your current boyfriend. Let him know that issues you are having in the relationship and how you feel the love is no longer there for you. Then you need to decide where and how to begin the new relationship if this is what you want.
Be prepared for hurt feelings.........while you can try and hide the fact that you were cheating a quick new relationship is going to be a huge red arrow pointing toward your behavior. The current boyfriend is going to be very upset with you and the new guy....he is going to feel like the new guy stole you away so be prepared for this and his hurt. The last thing you want to do is lead him on or make him think there is a chance.
Either way you must make a choice about who you wish to be with and then do so. It is not fair to either man to make them wait. In the end you could run them both off if you do not stand up and decide what you want.
I know this is hard........but the reality is you did put yourself in this position so it is time to deal with what has happened and make a choice.