Am I bisexual or gay?

Hi guys. I am new to this forum and after telling my story elsewhere and having gotten pretty poor responses, I thought I'd try this one as it seems to be popular and helpful.

Anyway, I am 23yrs old (male). I won't get into extreme detail about my entire life but from an age that I can't remember, probably toddler years, I knew that I liked girls. It was never a question. Throughout childhood and into my school years that continued. I had more crushes on girls that hot dinners and I remember chasing girls and trying to find a girlfriend as soon as my School days started. As life went on, I continued to have these crushes, I always wanted a girlfriend. In my senior School years (high school) I got my first real girlfriend (I say real...looking back on it now it was just childish fun...but at the time I thought it was forever...like you do). That ended...more crushes came and went, more girlfriends came and went and as my School years began to end I noticed that my friends were all starting to get involved with girls in a more adult way. So I found a girlfriend which happened to be in the most unexpected place...on holiday abroad. I met a gorgeous girl who I liked instantly but I thought would never even look twice at me. I got a couple of signs from her that she was interested, but she was younger and I knew little about her so the nerves got the better of me and I ended up returning home empty handed. A week later we spoke online and turned out she lived just twenty five minutes in a car away. We met and ended up together. It was my first real relationship outside School and my first time sat on the sofa with a girl in a house...watching tv with my arm round a girl. It felt unbelievable. But as time passed, it quickly became clear that we were still young, still a little immature and the travel distance for two people with no transport was becoming virtually impossible. It ended, and I was devastated.

About six months later, I started a new College Course...to try and better my education and find a career path as my School results were not that great. It was around this time, that I started to notice guys as well as girls. At first, from what I can remember, I didn't really think anything of it. I just thought of it as a bit of fun, fantasy...probably a phase. But even telling myself it was probably a phase, was something I never even thought about because it was just not important.

Very early into the College Course (age 18), I met a girl who I fell in love with very quickly. Luckily, she fell in love with me too. We lost our virginity to each other, which was unbelievable and our sex life from there, once that ice was broken, was very good. We had sex frequently and to be fair...I initiated it most of the time. We went on holidays together, bought each other expensive gifts for Christmas and birthdays, introduced each others families to each other...traveled some more and fell deeper and deeper in love. I was the happiest guy on the Planet. We stayed together, for two years. I was sure that we would be together forever and I think we both wanted that at one point. But unfortunately I was becoming, a little possessive, a little controlling whenever she mentioned male friends and a little worried that she could cheat. She left me in the end and if I thought I was devastated over my last girlfriend, this was like being dropped into hell. I stayed in my bedroom and didn't come out apart from if it was totally necessary, for six months. Every time the phone rang, every time a text message came through I would grab my phone and pray to god that it was her. But it never was. Before long I never heard from her again. Still to this day, I miss her, three years on from when we broke up.

Since our break up however and the three years I've had to be single...from 20-23. I have not bothered with chasing girls, I've not bothered with any of that but porn has been a major part of my personal life and with the attraction that I found from guys before I met my ex...I reverted to that because it seemingly turned me on, more than straight porn did. It was still however, not important. I put no store by it because the fact that I had been so deeply in love with a girl, was romantically, emotionally and physically attracted to her on many different levels, questioning my sexuality was never ever an issue.

Fast forward to August this year, age 23 and I am sat in the front room with my mum and dad. A man comes on tv and comes out of the closet as bisexual. He starts crying and its all very sad and uncomfortable to watch. My mum says "How awful for him...he is in his early thirties and he has never felt like he was able to be himself or come out and tell people who he is". As soon as she said that, something just clicked in my mind and every day since, I have been extremely paranoid over my sexuality. My attraction to men, physically, is too strong to be just a bit of fun and has gone on for too long to be, just a phase. So I know that I am quite likely to be bisexual. Since this incident with my mum though, I went back to watching straight porn...thinking that maybe I had gone down a route here and I could reverse it and go back to how it was before. Very quickly I noticed, that I had a very hard time getting an erection from straight porn. Switch to gay porn...and I get an erection no problem what so ever. But with straight porn, it feels like an effort and a strain and a pressure. Maybe I am struggling to get an erection purely because I am paranoid and I know deep down that even though I'm trying not to think about it and just relax...I always am thinking about it. So this could be unconsciously putting me off.

My question for you guys is that...I don't understand how on this Earth, I could be gay. I don't understand how all my life, I have been attracted to girls, to women. Then that all changes and suddenly, I am gay? I am scared of getting into a new relationship because of the chance of not being able to get an erection and this confirming my sexuality. But then I think...but what about the two years with my ex? People say porn is not an indication of sexuality, it is not real, purely fantasy and fiction. Maybe so...but when you are paranoid, that can be very hard to get your head around.

Thank you for any advice. I appreciate it.