You're asking if you can live without sex - well, only you and the future can answer that.
Some can, some can't. You could do a straw poll on mn, and find out what other people think but, really, it all comes down to you. Doesn't matter what works for other people. You have one life. And only you can live it.
If, on balance, you can live without sex because friendship, rest of your life, etc, cancel out the cost of no sex, then, I guess, you'll live without sex.
If not, then you won't.
Wrt OM - well, use it as a thought-experiment; what's it telling you? Be very honest. I have opinions as to what it's suggesting, but I think the exercise would do you good if you do it for yourself.
Yes, try counselling - but put in a little thought beforehand as to what, precisely, it is you want to explore. What would be your optimum shape of a relationship? What would you compromise on? These things are different for everyone - you need to work out what you want.
What do you want?
Wrt affairs ... well, you know, there's a lot of talk on mn about how people should act v. rationally about splitting up and I am well impressed. I have a few friends who have split up that way, but they are extremely conceptual people ... and it has consequently taken them years, and years, and years to separate, and a lot of talk, and a lot of counselling. And it demands enormous emotional literacy, enormous patience (of camel-like proportions), and a capacity to be extremely abstract. Oh yes, and enormous reserves of existential courage, too.
So, I cannot find it within myself to be harsh on those who do have affairs. I find I know too many people who are not so capable of such exemplary conceptuality and fortitude.
Most people don't have that. I am astonished and deeply impressed by how many there are on mn.