I must say, I never had the word divorce in my vocabulary. I despise the thought of it. Even when things were not going well, I wanted to work on things, not give up. Then, I discovered proof of the affair that I had suspected for a couple years...which was part of a lot of our issues. So, obviously as pointed out, there are plenty of reasons for a divorce. I would say that an affair isn't something that can't be worked through, but it would be really hard and would take a ton of commitment from both parties, one of which has proven they aren't so good with commitment. My advice outside of an affair is to try to work on the relationship with all you heart, mind, soul, and everything you have. It won't always work and there is no shame if you have given it the effort it deserves. Some people just don't work out.
I'll note that today would be (kinda still is I guess since it's not final) my 5th anniversary. Kinda depressing on many fronts.