You aren't weak. That reminder of betrayal by the person you have exposed your vulnerability to more than any other person hurts. We all steam along when thinking we are doing really well until our trigger gets pressed, then we sink down and realize we have more work to do.
You go on the date if you feel like going on the date. That's what should determine it for you.
You may want to write out a letter asking him for what you need from him to move past this affair and heal your M. Tell him that you have learned there are some things that make for healthier, quicker healing, which is something you know he probably wants. Those will require that he do some things in the short run that may be hard for him, but a little short run difficulty for faster happiness seems a good exchange. Lay out the things that are mentioned in DR & that Toots mentioned. Tell him that you will be glad to give him some of the reading (and assure him it is short) that will help him understand what the betrayed partner goes through and how both can speed and improve the healing process. The letter gives him something to read over a couple times and digest. It also catches his attention more than just another conversation.
I hope whether you go out on the date or not that you are feeling better soon.
Me: 50 W:43 S6, S3 M: 12 yrs. T: 17 M is bad & Not happy Bomb Mar '14 S 5 Feb '15 D Bomb 13 Apr '15 (but "no hurry") DB Coach May '15 Wants proceed on D Aug '15 Starting 1-on-1 negotiations Sept '15