Sexuality too Fluid: Does this happen to you?

I am a 29 yo Bi male from Dallas and I have been having some issues with my sexuality since I was 14. I recently have been comfortable with my same-sex attractions and have come out to some of my closest friends. (Especially those I knew wouldn't give a shit)

When I was younger I always figured I was straight and just had some weird sexual fantasizes about bottoming or sucking a dick. These seemed to be especially strong if I was on my ADD medication/other speedy drugs, but I thought nothing more of it.

As I got older I noticed that when I was sober I was finding guys attractive, checking out their ass, watching movies b/c of the male lead just like some of my girlfriends. I realized this was a real part of me and not some drug induced kink. During college I found out in a drunken conversation that my best friend was also bi, and just went for it. We ended up having amazing sex and fell in love with each other dating for a long time.(2 years) During this time, I figured I was just gay. I accepted that I was gay, I was ready to tell my parents. Then after the relationship ended (he moved away and got a girlfriend / got married) I found myself not getting into my gay fantasies. I was back interested in girls, Wanting the hetero normal lifestyle. I couldn't even jack off to gay porn, it just didn't do anything for me. I started thinking that maybe it was just a phase, but sure enough about 6 month later the feelings came back and I find myself browsing M2M personals on CL.

I know that i shouldn't be obsessed with labels, sexuality is fluid. I am proud to be able to appreciate love/sex with all types of people. But I feel less Bi, than I do Straight sometimes, and Gay sometimes. I have this horrible feeling that I have become a terrible stereotype. It's like I cant make up my mind.

Is there anyone who can relate to these type of feelings? How do you handle them if you are in a committed relationship? I have a big fear that I will meet someone and then loose interest in him/her and hurt them only to want it back at a later time.

Sorry for the life story, I just don't have very many opportunities to talk to any other Bisexual people. Thank you all.