Mia: Don't believe this "just a friend" crap. Your spouse is cheating on you emotionally and maybe physically. Otherwise, why the secrecy? Get to a marriage counselor. If your spouse won't go, threaten to expose what's going on by telling the fourth party.
Q: I hate my in-laws and I think they hate me. I don't want to spend the holidays with my in-laws, but my husband does. They come to town and don't even call us. Now they're having a big Thanksgiving dinner and he wants to travel 400 miles to spend the day with people who, when they come to town, don't even call. I don't want him to be a chump who's reaching out for love from people who don't include him.
Mia: Lucky you that the in-laws don't come around. But what about your guy? He loves his relatives regardless of how they treat him. So you have no choice but to go with him. Thanksgiving is one day. Just smile and keep your mouth shut. You don't have to see these people often, so suffer through it and know that you're doing it to make your husband happy.
Steve: Oddly, people after marrying often seemed surprised to learn they've inherited a whole other family and all its problems. Support your husband in his efforts with his family and, as Mia notes, be happy that you don't have to see them much.