Am I bisexual, heteroflexible or scared? Questioning male

Hello, thanks to anyone who's reading this. Any advice or responses would really mean a lot.

I'm a 20 year old guy currently completing my degree at college.
When I was younger (11-13) I identified as gay in secret, I never came out or felt attracted to any guys i knew in real life but I joined online chat rooms to meet other gay guys and was in a secret online relationship with a guy for a couple of weeks until I had to stop due to fear of being caught. During this period I was exclusively only sexually attracted to guys, but actually it was more like being sexually attracted to having sex with guys (i could only watch gay porn etc) as opposed to the guys themselves.

As I got older i sort of drifted away from that "scene", stopped using online chatrooms/forums and went through some pretty rough patches in my life but overall life moved on and I just avoided thinking about my sexuality. Since then I'v been in about 3 serious relationships (all with girls) and I know that I'm definitely sexually and romantically attracted to girls which made me identify soley as straight, but i'v begun to question that again.

I'v been single for the past few months now and have been dealing with feelings of loneliness and confusion. Sometimes I imagine having casual sex/dating a guy but it feels hard for me to imagine a long term relationship with a guy. Another thing is that while i definitely do feel sexual and romantic attraction towards girls, my attraction towards guys is unsteady and confusing.

Usually i can look at an attractive guy and think "wow he's attractive" but its not the same feeling i get at seeing an attractive girl. i'm not sure if its because theres some psychological block in my head barring me from being able to see myself with a guy due to my history of being so scared to come out/knowing i wouldnt have the courage too.

In terms of romantic attraction, i definitely feel like i am capable of being attracted to both sexes - i feel a little aromantic in that my romantic attraction to people is tied to knowing that they are attracted to me/feeling desired. I cant feel any kind of romantic attraction to someone unless i know they feel the same about me.

I'v never dated another guy in real life, but i have dated and slept with girls. I know i'm definitely not gay but i'm trying to figure out if i'm bisexual.

Another thing is that the thought of having casual sex with girls puts me off, but not the thought of casual sex with guys, in fact i really love the idea. Recently i'v really been considering going to a gay bar but i dont know if its a good idea as i'm quite self conscious and its all very new and i dont know if its a good idea to go alone?

I feel like i might be bisexual but am struggling because i'm only just starting to come to terms with/seriously think about my sexuality.
Is it weird if i can only imagine having ONS with guys, but not serious relationships?