I'm a bi guy in a longterm hetero relationship. I'll preface by saying that I would never under any circumstances cheat on my wife. But there are times where I do miss gay sex and typically watch gay porn to enjoy it vicariously.

Any other bi people in relationships that get this feeling?

From what Bi friends have told me, that's the hardest part of being in a monogamous relationship when you're Bi- You can only pick one gender to be with, and no matter which one you pick you're bound to miss the other one sooner or later.

Yeah that happens, I recommend arranging a three/foursome, if your wife is okay with it I mean