Conflicted (semi nsfw)

I am in a bit of a situation. I am a bi individual who is in a long term relationship with a woman I love very much, but who is not satisfying my more primal needs. I have. Sjtarted haviiing serious fantasies and urges to go out and mess around with a man. For some reason my brain makes this seem ok. I know it's cheating and I won't act on these urges, but does anyone have any advice on how I might quell them? Only recently have I had any interest in men(in my 30's). The urges are really to be me being forced/coerced into it. Kinda weird, but it is what it is.Could this just be me feeling imasculinated, or something else entirely?