Hm. I'm always suspicious of the 'best friend' that declares his love when you are IN a relationship. There is some kind of subconsious thing going on here most likely on both of your parts. There is something called secondary gain and I'm sure he has made your ego feel good in these past two years . . . and on some level you knew. But it felt good. Well, you must fight this urge dear.
If you are in a relationship that counts ----------- you'll need to tell your 'friend' that you never want to hear him say that again and he has no hope. Be clear with no room for you to act torn. Otherwise, you'll need to end the friendship.
Would it be difficult for you if your partner had a female friend that told him she loved him and wanted to be with him and wanted him to leave you . . . would you be comfortable with them being together anymore or friends? I wouldn't. Your "friend" just ruined the friendship. And I think one thing he was after was subconsiously ruining your relationship.
And if you do desire to be with ANYONE else other than your boyfriend, break up the proper way-------- take some time to get over it without dating anyone and if the "friend" is still available in a year----- go out on a date with him.
good luck
If you are happy in your current relationship, then why mess it up...we will all have temptations of other interests in life, stay true to the one you are with, and if that doesnt work out, you can consider your friends feelings down the road. If its meant to be with you & he, it will be..but dont change your life to try and make it happen , just wait, and if its meant to happen, it will.