Rainbunny - do not feel guilty. You did the right thing. By yourself, and any future children. It would have been much, much worse to persevere out of misplaced feelings of guilt.
Also, I think your case proves that the impetus to leave is often very different for women compared with men.
I totally agree with SGB's take on it. Women are often (broad generalisation) much more capable, able and self-sufficient within the average family set-up. They either do, or manage, the majority of stuff that goes on in the house, whether SAHM or WOHM.
Often times, this workload becomes intolerable, and so resentment sets it, which gnaws away at the happiness of the relationship. When it doesn't get resolved, the relationship breaks down.
And then, it is 'easier' (relatively speaking) for the woman to leave and got it alone, because she knows she can cope on her own, and in fact, being alone would be mich more preferable. She does everything anyway, and it's one less person to look after.
It is much more difficult for many men to make that leap, because they don't have the first clue/appreciation as to how much is involved in the running of a house, not the inclination to do any of it.
Hence, swinging orangutan-style onto the next relationship, getting a firm grip on the next woman, before releasing his grip on the previous.
Disclaimer: I am not talking about happy, mutually satisfying relationships, with kind, decent men. I'm talking about relationships that break down, and where one partner resolves that by cheating.