M-Kate right at the start of the Mindfuck, when I was confused, concerned, scared that I was losing the person I felt was the most important in my life I was twisting myself in knots, angry at myself that I wasn't enough for my partner.
But these men don't need the straightspouse to understand them....they need us to be okay with who they are and not have to take any responsibility for what it does to us. 
The bisexual man in my case could separate who he was with me and who he was when he was with somebody else, when he was watching porn or reading literotica. My concerns did not factor.

This part of the Mindfuck did a 180 the day I saw an lgbtq counselor. I made the appointment because I thought if I understood more from an lgbtq angle my fears would be less. The guy basically told me I should let him be who he truly was. No advice for me other than that. I'm so glad I did this. It hurt like a knife through the heart but y'know from that day on my need to understand him started to wane..
...and I began to want to understand me, what would happen to me and where I belong

Elle

LOL

The way I try to frame it is not by trying to understand how someone could be bisexual, but more by degrees of homosexuality. If you completely forget and discount the heterosexual nature or part of them (despite what some people may say, this is still largely normal) and look at how strong the homosexual urges are. You will see how strong a part of the identity it is. For some it is only ideation, they acknowledge a sexual attraction to same sex. For others, the attraction is strong enough that they feel the need to act on it. When they are “getting what they need” from a same sex partner they are not being bisexual. The same is true when they are engaged in a sex act with the opposite gender. The bisexuality is a passive state of being while the orientation is fluid. Men who are bisexual are sexually attracted to men and the other man’s sexual attraction to them. They could have submissive penetration fantasies where they are sexually attracted to being taken by, and inseminated by another man. There could also be the opposite attraction to be sexually dominating another man and be the one doing the penetration and inseminating. You could also have the balance of enjoying both roles. So, it is not so much to do with the physical sensations of heterosexual sex. But, more to do with passive and submissive emotional and physical roles combined with and leading to gratification. There doesn’t need to be an emotional connection in place for this to happen. A bisexual man can romantically love a woman and make a clear distinction between this as a relationship separated from his need to be sexual with men.

M-Kate wrote:

Thank you for your insight.  It's hard to wrap my head around.   I remember during one conversation with my husband, he said that he didn't always want to be the "fucker".  He wanted to be the one being fucked.   He also has said that he would like me to just fuck him and so we bring in sex toys.  I don't know whether I can truly ever accept this part of him.   

It is up to you entirely as to what will accept. I can also understand why it would be difficult for a heterosexual woman to penetrate her husband. Normally it is the man’s masculinity that is an attractive quality and not a submissive brand of neo-femininity. It is also difficult for me to understand why a man would want to be “fucked” by another man. That in doing so he would find some pleasure from being dominated. But, I would certainly be concerned by his actions in respect to your health Kate. A woman in my group was left distraught by the fact that not only had her husband been off getting fucked by men. She also got the extra gifts of syphilis and Hep B. She sobbed with the shame of his bisexuality and the shame of having STDs. I am sure you would be happier with a straight man, who would be more than happy to ensure that you were the only focus of his desire and affection. My heart goes out to you.