My husband is going through midlife crises at age of 30. I'm very angry that he is throwing away all that we had worked for over the years, and very angry about what he is doing to the children. I think it is a mid-life crisis because he wanted to re-experience that feeling of romantic love that he remembers from years ago when he was younger.
Today as it seems midlife crisis is used to brand any type of unsuitable behavior within a marriage, even if the person is years away from midlife. Being a cheater at age 30 isn't having a midlife crisis, its disrespecting marriage vows. A husband who at age 30 search for his "true love" outside his marriage might be in the grip of a midlife crisis. It isn't a medical condition that is easily diagnosed and cured.
Girl, you're supposed to get angry because he's cheating on you! It is a crisis that he's breaking the vows and consequently, your heart, but it's not a midlife crisis that he chooses not to be faithful at this time. That was a moral decision on his part, something that was made consciously and purposefully. Better to know sooner than later, right? Don't make excuses for him, I'm sure he does a good enough job of that.