How can I possibly break off a relationship with this guy...? :(?

I'd suggest you talk to him about this, explain to him how you feel. The worst way to end a relationship is leaving the other person without an explination, which could cause irrationality and sometimes cause un-true rumors start. If he takes it to the extreme, or gets upset, then it would probably make your decision easier. If he tries to work things out, maybe try and work things out with him and see if you two can even make the relationship work with the current problem at hand. Being 'stuck' in a relationship can cause problems in later relationships. If he's mature about it, and wants the best for you, he will let you let him go.