I need to make sense of my Sexuality!

Hey guys, I've been struggling with the issue that I could be gay, bi or straight. This could be a bit long and I have tried to put anything that maybe of relevance to it in. It started a while back when I was at work. One of my colleagues (who is gay) asked me if I was gay or not (I have been teased before about being gay, and have never been troubled by it before) and, as always, I ignored him and carried on with the task at hand. Then he said the thing that started this mental torture. All he said was "you didn't deny it, therefore you are gay!". At the time I didn't take much notice of it. Anyway for some background info, I am an 18 yr old guy, I have never had sex but have had sexual encounters, I am not homophobic, I kissed my best friend twice because he wanted to check whether he was bi or not, I did not enjoy the kisses and broke them off almost immediately. I have also tried for relationships with girls before hand and have either been rejected at first or lead on and let down before the first date. I have had major father issues when I was 10 up until recently and have not seen him by choice. I have seen both of my parents naked. I also have been very sexually attracted to girls up until recently but during certain days I still get aroused by them and when I masturbate to porn or fantasies with girls in them I orgasm but it takes time to get a hard on, whereas with guys I get aroused when I think about gay porn but I watch it jerk off over it but I ejaculate but I don't feel any pleasure. I have done this numerous times sober and drunk with the same results. I do look at guys and go he's good looking, more often than I do with girls but this has happened since the incident at work. At the beginning it was easy to ignore but it has slowly manifested itself to the point to where I am completely confused about my sexuality. This problem has been going on for roughly a month and a half and it took a month before the work stuff happened that I started to question myself. The other side is that I can imagine me doing stuff with guys and girls but I don't like the idea of kissing a guy and most the time do not think I would like a relationship with a guy. Another problem is that when I thought I was gay over my 18th I went out for drunk, made out with a girl and wanted to sleep with her but that materialised. Also all of my dreams involve me being with girls and wanting more, and on the occasion there is a dream about me being attracted to men I always said no. Sorry for rambling on but I hope all the information someone can make clear for me because I have tried for ages to make sense of it all but I have been unsuccessful. So the simple question is what is my sexuality?