Questioning Hard And I Feel Awful

I've always been straight (strictly attracted to women) until last night. I had a dream where I was giving a blowjob to a guy. I woke up very turned on and masturbated to this thought. Now I've fallen hard into wanting to fulfill this dream and have it reciprocated.It's a weird feeling because I've been so sure of my sexual orientation for my entire life and now I don't know how I'm feeling. I'm in a serious relationship with a girl and we've talked about our future together. We seem to be on the marriage/together forever track.What scares me is that either I live the rest of my life regretting not following this desire or I have to break up with this girl and break her heart and mine.I know I have to decide what I'm going to do myself but if anyone has any advice/encouragement/questions for me to ask myself, I would appreciate it.