Long distance relationship - BF arriving but fallen for another boy. What to do?

Here's the question - if you're in a long distance relationship (I mean different countries, 3000 miles apart) and your BF is meant to be coming over to spend the summer with you (flight booked), BUT you've been getting to know another boy over the past few months and are falling for each other fast, what should you do?? Be honest with the BF and tell him not to come out? Is it better to be truthful and risk hurting him badly? Or go with the original plan and try to forget the new guy?