If Tommy hadn't kissed Buck in 7x04 I don't think Buck would have realized he was attracted to him. Oliver has said that Buck has felt this way before and Buck has always been bisexual, he just didn't realize it and it was the kiss that prompted that realization, not just Buck's crush on Tommy. If it was just the crush on Tommy Buck would have realized he was bisexual way earlier.
Just today Oliver said that Buck was probably attracted to Eddie when he first met him and he didn't know what those feelings were or how to process them, so he acted out.
The difference between Buck meeting Eddie and Buck meeting Tommy is that Tommy is queer and knows it and can see the signs and signals that Buck didn't even realize he was putting out there so he kissed Buck. That was the moment Buck realized he wasn't straight.
And throughout the episode Buck is shown to be jealous of not just Tommy, but also of Eddie. There are so many moments in that episode that make you wonder who he's jealous of and why.
Is he jealous of Eddie for spending time with Tommy, this cool new person they met? Yeah. Is he jealous of Tommy for spending time that he views as his with Eddie? Yep. Is he concerned that Tommy might be taking his place in not just Eddie's life, but in Christoper's? Yes. Is he just general confused because he's feeling some type of way that he really doesn't understand? For sure.
It isn't as cut and dry as "Tommy was Buck's bisexual awakening" full stop, because we've heard Oliver say that Buck has always been bi he just understands it now. We've heard him say that Buck was attracted to Eddie when he first met him but didn't understand it. We heard Buck tell Maddie he checks out hot guys asses.
I fully believe that if Tommy hadn't kissed Buck in the loft that night that Buck would have written his weird feelings off as just new friend stuff like he probably felt for Eddie and has felt for other men but didn't understand and eventually he would have gotten over it.
Tommy's kiss was the catalyst for Buck realizing he isn't straight, but it wasn't just Tommy that made that realization possible - it was Buck's entire life that did. It was him talking to his sister and her affirming him and helping him understand that checking out a hot guys ass isn't abnormal, but it isn't straight. It was Buck looking back at his past feelings for men and realizing that they're similar to the crush he has on Tommy.
And this isn't me devaluing Tommy in Buck's coming out arc, because without that kiss Buck likely wouldn't be here yet. But I think saying it was all about Tommy and Buck's jealousy in 7x04 was only about Tommy is doing a disservice to the nuance of the episode and Buck's sexuality in general.