I find that the toughest part about growing, is when you outgrow your friends.
I remember a friend of mine telling me that the first thing that an alcoholic needs to do in keeping their sobriety is to get new friends.
"Why is that?" I asked
The answer was, "Because all of their old friends are their drinking buddies."
You see, just because one person decides to get clean, doesn't mean their friends want to. When one person is making a change that they feel is going to be better for their lives, it may not work for the others. That change is always inevitable in our relationships. We change because our circumstances and environment changes. Because our journeys are all different, it alters what was once workable for at least one, if not both parties involved.
The toughest part for me is the history that you share with that person. Someone you loved as much as you thought it was possible to love another person. If you truly love that person, I would think you would let them travel their own journey without you, knowing that they will always carry the time you spent together with them.
Indeed, perhaps letting go of a relationship is showing that you truly do love them...