Totally helplessly in love with someone, but in a relationship with someone who is pretty great

I love my girlfriend. She is kind and has never done anything to hurt me. There is no reason to break up with her at this point. We're both about to graduate and will potentially not be together in the summer, but I feel like it'd be cruel to break up during the last semester. I've kind of reconnected (not in a sexual way, I would never) with an old friend from high school and it's just killing me. She's really perfect and makes my heart get light when I see her. Everything about her makes me excited, but the crazy thin g is that it's not coming from a desire to sleep with her. I have fantasies of like talking to her over coffee. I am worried i might be feeling like this just because I know my relationship might come to an end soon with my current girlfriend. Do i owe it to her to stick it out, or do i follow my guts right now?