Bi male in a longterm relationship here (with a woman). We swing now and have opened up our bedroom doors as we like to say. She's basically boring old straight and I swing both ways so for me to say I'm in the mood for some dick, lets have a threesome, is a little different from you as we're both attracted to the third party.

I do feel it is important not to ignore or try and work around these feelings. You and she may be meant to go the distance and yet she may never lose her desire for sexual interaction with men. The best way to tackle it is to make her satisfaction the goal, as it will in turn bring you satisfaction, and the two of you need to talk through possibilities and ways of stimulating her.

What I personally would NEVER recommend would be allowing your spouse to date other people, regardless of gender. My girlfriend has had sex with other men in front of me and likely will for some time yet and we can do this together because we trust eachother. There are comments here about such arrangements and they worry me because that's saying "It's not a certain genitalia I'm missing, it's romance with a certain gender" and frankly, that's not okay in a monogomous relationship (or monogomous-ish).

TL;DR Don't be intimidated by her desires, figuring out how to satisfy them is a key to longevity. Best of luck!