Hi,
First of all you should decide if that "new" guy is what you really want and if he is "worth" breaking your present relations. If you are sure about it than finish nicely your present relations. I believe that if one wants something one should be proactive and take the initiative (nothing will, most probably, happen if one sits aside and hopes). If I were you I would simply let him know. The best way is to do it face-2-face (shows you have a character and courage) but you can send him an e-mail or snail mail..... Don't send someone to do it for you (can make a mass out of it). Please note that he might say no... and you know what it means...
Best regards,