The biggest surprise was how much masculinity turns me on in a men. With girls I've always liked to dominate so I'm also pretty masc.
At the time, I didnt even know if I was bi and was going through the usual gay porn jerk of then feeling guilty cycle. I was at the Uni and in the gym's locker room, there is a spa and sauna where people go in nude. My first big surprise was how I enjoyed being watched/cruised by older or more masc looking guy. I didnt even know what cruising was but I surely enjoyed it when a guy would try to touch my legs in the jaccuzi, but I would always ignore them while letting them do their thing (just some light "accidental yer voluntary" touching). One day, everything changed. I got to the locker room and there was mid-fifty dude, greek god body good looking and very straight looking. I walked into the locker saw him putting his shirt on (he already had his pants on) and maybe I starred a bit for too long at his amazing pecs ans 6pack. For some reasons, I walked towarda him and picked the locker next to his. I changed up then went to pee ( my innocent/naive self was hoping that he would follow). He actually did follow and went to pee next to me, then I noticed him stare at my dick which was already semi hard. Without even talking, he looked me in the eye, then I stepped back to let him play with it. He asked me to follow him in a more discrete/hidden restroom, he went down his knees and sucked me dry. From this day, every time we would see each other working out, we would ignored each other and the first one that finished the work out would make sure to pass by the other as signal that "I'm ready for you". He probably sucked me a good 10-20 times. Only disappointment was that he would not let me suck him, I tried to play with his dick but he could never get hard. On the other side, his cocksucking skills were out of this world. Excellent ! - Then my interest in dicks was confirmed, and when I would go to the sauna, I would start cruising.
My second big surprise was how submissive I am and how much of a size queen I am (ie. I like big dicks). The second guy, a ripped asian guy (probably from thailand) made eye contact and I followed him. The guy had a big and thick dick ! Probably above 8.5" easilly. While the first dude became my regular cocksucker, I became the second dude's regular cocksucker. Eventually, had a third guy that occasionally would be in the showers at the same time with a huge sack of balls - but I always kept him as last option if the other 2 guys are not there.
This leads me to my 3rd big surprise: that I am not only submissive, but the idea of being someone's personal slut gets me going.
This lasted for about 2 years until I became so guilty and thought that I turned gay and that I would never be into girls if I kept doing this. I was able to last for 2-3 years without submitting myself to what I thought was this toxic/guilty pleasure. To be frank, I'm impressed that I was able to keep it contain for that long by occasionally watching gay porn. Fastforward to now where I now know that I am bi and comfortable with my sexuality, I dont know if I could contain this "perhaps too occasional" urge.