Believe I'm bi and want to come out but need to be fully sure

So I'm 21 and male and I've been taking my time to fully figure out my sexuality. I've never really worried about what gender I fall for but I currently feel like coming out and I believe I'm bisexual but feel I need to be 100% sure as I don't want to come out and then backtrack what I said and replace that label with something else (I hate labels, but I feel I need to have one in order to connect with my family and friends about my sexuality as it has been taking a bit of an emotional toll on me recently).

Basically, growing up through my teens, people in my class were clearly starting to discover their sexuality, but I never felt I was getting the same feelings as everyone else. I felt like through puberty I had to get sexually attracted like a maniac with boners popping up at every girl I saw, but I never really got that. I figured I could be gay, except none of that was happening towards guys either. I didn't really worry about it since there was no point to worry over something that wasn't there.

I did get crushes on girls in my class throughout my teens, some where small flights of fancy while others bigger, where I wanted to go out with the girl and spend time though I was always underconfident. Friendwise I was fine, I'd have best girl friends, and best guy friends, and it had alternated that way ever since I was a little kid.

I'm not saying I never got boners, I just felt I never got them the 'proper' way, to the point where for a while I felt I was asexual (and practically that's what everyone called me). I did turn to porn and initially focused on heterosexual porn. Later on, I realised I preferred porn where both the man and woman where attractive, and this led me to checking out gay porn with which I was perfectly fine and I'd alternate between the two, though since then I do have a preference for the gay porn (not gigantic, but it's there).

I did have situations where it felt my girl crushes would go somewhere but it never worked out mostly due to timing (as they occured at summer camps and I wound up letting sparks fly towards the end of our time together), but I never really had time at school and never fully focused on relationships. I figured I'll have the time when I leave school.

I've now been out of high school for a while and my first year out I didn't really find anyone. There was one girl but she was already in a relationship so I let that go. The following year I got big crushes on 3 girls. One was once again in a relationship, one got with another guy over the course of the year, while the 3rd one I saw only from time to time. These weren't simultaneous but more like followed one after the other over the course of the year. I felt both emotionally attracted to them, enjoyed spending time, but also wanted to get intimate sexually, and I did have dreams about them and fantasized. But at the same time I also had minor crushes on 2 guys on the course. I couldn't see myself in relationships with either of them, it was more on a physical level, but it left me confused and unsure of pursuing anything.

Now I'm on a new course so everyone from the above paragraph has moved on. And I've gotten to know people from the new course. And there's only one person that I feel a possibility of a relationship with and it's a guy and it feels mutual. I want to pursue it but since it'll be a same gender relationship, and due to pretty much lack of anonymity thanks to facebook, I want to come out to my mother and sister (kinda not sure if I wanna tell my dad yet) and my friends, instead of them getting news of this through some randomer.

The part that confuses me is that now that I have a crush on this guy, it's really all that's on my mind relationship wise. For some reason I feel like I'm betraying my belief in my bisexuality because I believe I've temporarily dropped my interest in girls, and am in a way worried that if I come out as bi it will never come back and then I'll have to be like "Hey, I guess, not". And I feel that because of this crush I've suddenly gone full gay. Guess I'm curious how this compares to others experiences?

I can see myself in relationships with both a guy and a girl, and also sexually enjoying both. And I'd be perfectly fine if all I ever had were girlfriends, or if all I'd ever had were boyfriends but I feel a weird obligation to justify both sides of my bisexuality. To be honest, writing this all out I feel pretty confident in my bisexuality (with a bit of graysexuality mixed in? Or just a low libido - which has also always worried me about whether I am in fact just gay, even though the low libido thing happens with both genders), just need a bit of a confidence boost, as I feel that coming out may heavily impact family dynamics. I think my family is pretty tolerant, but having been brought up Catholic, I'm a bit worried about what people like my grandparents and aunts and uncles will think, as I don't want to impact family events like Christmas etc. as we always all get together.

I'm basically here for some advice, comments and support, as I have basically come out to two friends I lived with in the past year, though I felt I was met with a reaction of "Well, we'll give you time to fully decide on whether you're straight, gay or just plain asexual but wanna seem sexual" which didn't exactly fill me with confidence especially since they had become two of my closest friends. Another close friend of mine once commented on a friend of hers I don't know who said he was bisexual and was with a guy but according to her "Once you go gay, you're gay" so I've never felt like I've had friends I could confide in before my family. So here I am, internet. Hope this wasn't too long, and I'll appreciate any comments.

(Apologies if double post but I don't think this posted the first time...)