I'd try not to talk about your decision or the R if you can. Certainly, you shouldn't initiate. If he asks, just say you don't feel comfortable with the arrangement any more, and that he has to demonstrate that he is done w/ OW & work to rebuild trust. It can be done, but he is going to have to commit & demonstrate that he will stick w/ it and work on the M before you see that happening.
Don't worry about the anniversary at this point. A lot can happen in the next two months. Esp.. if you haven't in the past years, it would be odd when you are having such trouble to try to give it meaning that isn't really there (at least at the present moment). If things work out, you'll both probably start celebrating the anniversary in future years with a new meaning. I'd wait for that myself, but you have to see what feels right to you when the time comes.
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