Doing stuff with another guy doesn't make you gay. I am gay, so using the "mess around with another guy = gay" logic - then that would mean if I mess around with a girl then I am straight.
Let me just say,
I am not straight. I have messed around with straight guys, mostly in high school, and they were pretty much just curious. They liked the attention, but allmost all eventually got bored messing around and I had a couple say "sorry but i'm not really into this anymore". Their curiosity fulfilled, they moved on.
Straight/gay/bi - I really like the percentage scale we have on here, that is a good way to judge
For the HIV comments - Unprotected sex/promiscuity/drugs sharing needles all are causes of HIV because all are responsible for spreading HIV (we should all know this by now) Unfortunately all of those things are popular in mainstream gay culture, especially before we knew about HIV, we (gays) didn't know we needed to use condoms back when it first appeared. The gay community did a great job of becoming aware and being safe and massively reducing the spread, our numbers were way down for a while, but that cultivated a sense of security and promotion of awareness dropped, we let our guard down/younger generation that are less cautious/aware, and now it is rising again in the gay community, although at the moment it is highest in the hetero black community (or at least it was, but i heard that a while ago so it may have changed).
That is a major reason why i do stuff online, it is the safest sex, lol. I won't fool around with someone unless they get checked for STDs and HIV and then show me a report from the doctor saying they are clean, this is because people lie. I have friends that don't tell (one now, a few in the past) that they have something, one in particular, so I play it safe, (although i will jerk, as no real risk of catching anything as long as you dont make them cum) but eventhough they prove clean, always use a condom