Limbo, it's amazing how often this behaviour happens when someone is cheating - something I never knew about at the time, more's the pity.
It seems absurd but there's a kind of relief when you realise there was a reason for the anger, the finding fault, the criticism and the stress. It's horrible while it's going on though - I felt like I was withering. What didn't help at the time was that two of my new business clients were also behaving very badly towards me (something I hadn't experienced in all the years I'd been running my business) and at times, it felt like the world was against me. Thank goodness for my friends at that time - had it not been for the positive strokes I got from them during this period, I might have gone under.
Mine did no projection about cheating (far too complacent) but he was uncharacteristically interested in an exchange of innocent E mails I had with an old male friend - at about the time he was also exchanging E mails with an old colleague (who later went on to be OW). So, probably a bit of projecting there too...
Like others have said, don't let this go on if you can help it. You'll probably be met with a denial, so in your shoes, I would be trying to find evidence. The phone is always the best key - but look for a second one. It seems that very accomplished cheaters tend to have a second phone on the go.
Also, try to pinpoint when you first started feeling unsettled - often the best clue is about how you were feeling yourself. Cross match that against what he was doing at that point.
If I'd been a member of Mumsnet in 2008, I would have been suspicious much earlier on, but the "infidelity clues" I'd read about just weren't there - it does seem to me that often, adulterers behave differently these days.