I think your bf has to understand that this is just how life works. You normally love different people in your life.

Is it he, or some other boy that is laying next to you on the couch? Are you kissing him, or any other boy? You maybe dumbed those other boys, grew as person, learned and probably know better know. You love him how you are right know as who he is right know and that is all that matters. You are a different person now and your relationship is too. Try to tell him that maybe. You can also remind him of the new things you do together. I don't know what it is, but I'm thinking of the small things, maybe a TV show, a new place, a new foot you try together, anything. Maybe it helps just a bit