Be honest with guy number one as soon as possible. Then he has enough time to ask someone else if that's what he decides he wants to do.

This is where you start to learn about growing up. First, you must honor your commitments. So for now you are obligated to go to the ball with the guy you agreed to go with, notwithstanding that you seem not to like him all that much and that you are starting a relationship with a new guy. This might help to teach you about saying "no" in the future when that's what you need to do. Second, you need to set boundaries with people. I don't want to say "this is a possible way to get out of your commitment", but ... it might be. Tell the guy who's constantly texting that it's inappropriate and that he needs to lighten up. It is okay to tell him that you have a boyfriend, and even that you would prefer to go to the ball with the new guy ... but that you will honor your earlier commitment to go with him as you already agreed, and you will have a good time anyway, and hope that he does, too. But also be clear to him that the texting has to stop, unless it's something "non-relationship" (like texting about schoolwork and plans for the ball -- occasionally! -- is okay, but you are NOT his girlfriend). It's not okay to tell him "I never wanted to go with you anyway"; there is no excuse for being intentionally cruel to him. Third, if you think you can manage it, you could offer to help him find a date for the ball who would prefer to go with him, and who he might like, too. But this is tricky, and could blow up even worse. I don't advise it, but it is a possibility if there's enough time and you know of any mutual attractions, even though unexpressed. So my advice is to go to the ball with the guy who asked you first -- because you agreed to. Be gracious, and don't snub him during the ball in favor of the new guy or anyone else. Have a good time and be cordial and pleasant with your date, but be clear to him that this is a one-time event, and he is not to read anything more into it than a single event. And learn your lessons for the future.