I'm in a relationship, but I like someone else???

Long-distance relationships are very difficult, and most are 'unsuccessful' and/or not long-lasting, when you're relatively young (And even when both people are older), if only because there are few ways of meeting up, which is almost-without-exception such an integral part of a romantic relationship. Given that you're both also still hugely growing both physically and mentally, it might be best to cut off this relationship. You both can still be very good friends for each other, but to commit yourselves to this huge — and honestly sometimes draining — commitment while you're both undergoing immense maturation may be to the detriment of both of you.

Regarding other people you are and will be interested in... they may or may not like you, even if you guys are technically compatible. Just as how I'm a gay guy who isn't attracted to all guys, they may not be attracted to you even if you were someone they could theoretically go out with. That's not meant to be a negative thought, though. Sometimes, the best way to live life is to go with the moment and the flow. Things may or may not happen with Steven. I'm sure that there will be other opportunities for you in the future, regardless, though.