WHEN I FOUND out my boyfriend of four years was gay, I felt a mixture of relief, disbelief and incredible guilt.

He was the first person I went to with a personal crisis. But he struggled with his anguish alone.

I learned that he was with men during our relationship after I confessed to cheating on him. He told me he was unfaithful too, also with men. He insisted he wasn’t gay; he was bisexual.

I believed him when he said he wanted to stay together. Until that point, our relationship felt close to perfect. Breaking up was not something I considered. I saw our indiscretions as simply a need to sow our wild oats.

So we both continued having affairs. We convinced ourselves this deceitful arrangement could work. But, of course, it didn’t.

We finally admitted that we needed to break up when I fell in love with another man. My former boyfriend and I became best friends and roommates.

But even after we split, he still would not acknowledge being gay. The grayness of his sexuality infuriated me.

I wanted to understand how our relationship deteriorated. If he was gay, then our problems made sense. I kept expecting a meteor of revelation to hit us. He’d come out and admit our relationship was a lie.

But our relationship wasn’t a lie. He was in love with me, and for years, he was sexually attracted to women.

I once felt so desperate for answers I actually Googled: “I’m gay but I like having sex with women.”

Results: None.

PEOPLE WHO come out to their straight partners are often seen as liars who want the comfort and acceptance of a “straight” life.

Author Terry McMillan filed for divorce from her husband, Jonathan Plummer, who inspired the 1996 novel “How Stella Got Her Groove Back.” Recently, McMillan publicly accused Plummer, who is gay and from Jamaica, of marrying her to gain U.S. citizenship.

“One of the biggest myths is they did it as a cover, as a way to pass in the world,” says Alex, a member of the Washington, D.C., chapter of the Gay Married Men Association. Alex spoke on the condition that his real name not be used.

He is married to a woman and they have three children. Alex told his wife he was bisexual before they got married.

Over the years his attraction to men grew, but he still tries to remain monogamous with his wife. They still enjoy an active sex life with each other. Even though Alex’s wife knows about his desire for men and his past affairs, they want to stay together.

“Many men find themselves in their 20s, 30s and 40s realizing, ‘My sexuality isn’t what I thought it was,’” Alex says.

That was the case for Philadelphia resident Joanne Fleisher, a social worker who counsels married women who come out as gay. Her book, “Living Two Lives: Married to a Man and In Love with a Woman,” is due out this fall.

“I had no suspicion or inkling of being gay,” says Fleisher, who described herself as “boy crazy” when she was growing up.

Toward the last few years of her mostly happy 12-year marriage, she fell in love with a close female friend. Fleisher and her husband, who have two children together, went into therapy to try to save their marriage but soon realized they should divorce.

Many women like Fleisher leave their husbands while still struggling with ambivalence about their sexual orientation.

“I left my marriage without having a sense of being gay,” she says.

For women who come out in marriage, their guilt can be overwhelming, Fleisher explains.

“This is a tremendous ethical dilemma,” she says. “It’s very different from other women coming out, because the decision involved is no longer a question of personal happiness. It ultimately will have a serious impact on the people that she loves.”

An overriding sense of responsibility to the ones they love is common among people in heterosexual marriages who struggle with being gay.

When Vince, who asked to be referred to only by his first name, acknowledged that he is gay, he became severely depressed and even contemplated suicide.

“I had decided it had been better for everyone if I died,” he says. “I had my plan in place, my method.”

Vince says he successfully suppressed his attraction to men for most of his life. He never acted on it. But at 41, the terrorist attacks of Sept. 11, 2001, forced Vince to face the truth.

He often took the flight that was flown into the Pentagon.

“It shook me to the core,” he says. “That could be me, and I could die with my wife never knowing the truth.”

Vince finally told his wife he is gay and hoped, naively he admits, that they could stay together. His wife disagreed, and they separated.

But Vince says he is like many married gay men in that he doesn’t regret marrying his wife, but does regret the pain he caused her and their children.

“I sure enjoyed the 20 years with her,” he says. “I wouldn’t have wanted to miss that.”

The gray areas of sexual orientation can be the most difficult part for both spouses in a gay-straight marriage.

Most important for the straight spouse can be a need for clarity. Several say they had an endless stream of questions for their spouse upon hearing the news.

“Why wasn’t there any intimacy? What was wrong with me? Why was he depressed? Why was he withdrawn? Why did he think he was in a prison?” says Amity Pierce Buxton of the Straight Spouse Network.

Buxton’s husband of 25 years came out after they separated.

I harbored my own set of questions for my ex-boyfriend, who is still a close friend. Since he came out, he patiently answered the questions he could.

But some will always remain elusive to both of us—like just how did this happen?