That was a difficult conversation for me to figure out what to say, and probably even more important what not to say. I always thought that my son figured out that my ex had an A, but after that conversation I don't think he ever put two and two together (even though she once told him that the reason I had been so upset about something was because I didn't like her having a friend of hers).
Coconut,
I'd bet your son knows exactly why you and your ex-wife divorced.
Coincidentally, this morning I read a Psychology Today article about the impact of divorce on the children. The author mentioned that children of divorce have a higher probability that they'll be divorced as well. (Divorce is the gift that keeps on giving.) One of the things that the author said that really struck me is that, because she'd been through her parents divorce, she didn't view marriage as something that's permanent. I decided that I'm going to have a talk with my sons, probably several times, to make certain that they understand marriage is meant to be permanent, in sickness and in health, and to make sure their potential mates understand that as well. I don't know if it'll make any difference, but I'm going to do my best to emblazon that on their brains.