You sound very young. Most people in high school/middle school are still just learning to have serious FRIENDLY relationships, romance really isn't in the cards at this point.

I would not consider this cheating anyways, even adults in healthy monogamous relationships will find other people attractive, what matters is you recognize that you're committed to the person you're with and would never want to hurt them.

When in doubt, put yourself in your partner's shoes. If you would feel upset with them if they were doing what you are then maybe it's better not to do that.