It's not always that easy and there is plenty of denial involved, says Amity Pierce Buxton, the founder of the support group Straight Spouse Network.
She started the group after she learned that her husband, from whom she had recently separated, was gay. "I thought he was a latent homosexual," she said. "He just repressed it and didn't tell me about incidents earlier in his life. We separated and then he came out."
When Buxton started talking about her experience, she found out how many women and men had been through the same experience.
"The first reaction is shock and disbelief and some relief, because it explains some unspoken problems that seem to be lurking there," she said. "The biggest shock is not the revelation but the fact that they've been betrayed and deceived for so many years."
Gay men are more likely than gay women to come out the closet, says Buxton. Therefore, it's more common to get calls from wives who find out that their husband is gay than the opposite. That ratio is slowly changing. Five years ago, one out of every five calls to her group came from a husband whose wife had come out as a lesbian. Now, it's closer to three out of every 10 calls, says Buxton.
Many women who may know or suspect that their husbands are gay are in denial, says Kaye.
"Women are very uneducated about homosexuality," she said. "They feel that even if men have done something in their past, if they can perform sexually, then they really have a straight orientation. But they'll always be living in the shadow of homosexuality in their marriage."
In her book, Kaye included "The Gay Husband Checklist," which lists ways for women to detect whether or not their husband is gay:
If your husband thinks you are a nymphomaniac or "pushy and aggressive" because you want sex twice a week.
If sexual activity steeply declines within the first few years of marriage.
You're always more sexually aggressive than your husband.
If your husband is turned off by the thought of touching your vaginal area or performing oral sex on you.
If his best friend is gay.
If he hangs out in gay bars.
If he enjoys watching gay porn movies and surfing gay porn Web sites.
If he is excessively homophobic, mocking and imitating other gay men.
If he brags about gay men complimenting him on his looks.
Buxton is skeptical that there are clear signs of gayness. "Straight men like to cook and decorate and there are gay men who like to do construction work so it's hard to generalize like that."
For the last few months, George, the closeted husband and recovering alcoholic, has stopped having gay flings.
"I would rather stop this behavior than go through a divorce," he said. "I don't want to ask my wife to be in a marriage with me where she's sanctioning me to go out and screw other guys."
Over a year ago, George started a blog to describe his experience and he soon connected with plenty of other men in similar situations, which he likened to group therapy.
He was on the verge of coming out to his wife when an online friend told him about his own experience with having a gay father. When the friend was 7, his father divorced his mother because he was gay. It devastated the family.
"I need to look at my responsibility and the impact on my children," George said. "Do I really want my daughters to see me throw their mother in the trash can? I can see myself married to my wife for the next 20, 30, 40 years. … And I want her to be my wife."