Falling back into love with my first love. Is this wrong?

As long as you have a boyfriend, I don't think it matters what he's thinking. Those five years did happen, along with whatever caused you to lose interest in him in the first place (funny how that seems to keep happening to your relationships), and it's not fair to either of your current significant others to pretend that you're unattached teenagers again. Stop the contact for long enough to figure out what's gone wrong in your relationship that's leaving you vulnerable to this infatuation, and decide whether it's worth fixing. If it is, let your boyfriend know how much of a problem it is that he doesn't seem involved in your social life (or whatever the problem is) and work on that. If it's not, break up and let your first love know that you'd like to see where things go if he's willing to take the same step. If it turns out he's not interested in leaving his girlfriend after all...well, at least you're no longer in a relationship that isn't satisfying you and have complete freedom to look for something better.