believer

I have no idea how long you should keep trying, but I do think it's important that you feel you've done all you could so you don't have any regrets no matter which way it turns out.
I also think you should try to focus on yourself

Swedish I think nailed these 2 points on the head. If there was a text book answer for how long to try -we wouldn't need all those self help books or therapists. But every situation is different & everyone's emotional reactions are different. There is text book "stages of dealing with loss" but that too - they say everyone has their own timetable & some go out of the "traditional" order. I think - just like - Swedish - as long as you feel that you have tried & exhausted all your options - then at that point you can feel comfortable making a decision.

The point about working on YOU - is also soooo important. One it is a way to rebuild your self- esteem after a blow of finding out about an affair. It will help you to love yourself, teach you respect of yourself & whether it is in this relationship if you continue or in a new one. YOu will better know yourself & therefore be able to know what will make you happy in this relationship or in your next. And to not let yourself settle for anything that doesn't make you happy. You deserve it!!