How do you become bi?

I have always had the desire to fuck and be fuck by a man. I want to suck cock, I see penises and find myself really wanting to touch It! But I am straight 95% of the time... What is weird though is that as soon as I blow my load and don't want a bar of it... I have a Mrs and she is not keen on this side of life, see has fucked me before with her dildos and this freaked her out a little. I don't want to cheat on my partner so I refrain from acting on impulse but it's starting to get difficult.... I have suggested a threesome with another man but she says it would disturb her to see me with a guy...