It's been my experience that life is a series of both joyous and sorrowful events. Making a new friend leads us into new experiences that we might never have known. It enlarges our tribe and contributes to our well-being. The loss of a friend, due to a myriad of reasons (job change, divorce, illness, death, disagreement, etc) is a fact of life. It's painful. It hurts. It causes us to question everything about the relationship.
The Five Stages of Grief are very real, and no doubt you are feeling them now. I recently lost my best friend of fifty six years to cancer. I can't change that. But I can reflect on all the great times we had and that cushions the pain to a degree.
I am also estranged from my brother and one of my two remaining sisters. They refuse to accept my transition and as much as I'd like to have at least a civil relationship with them, its unlikely they will ever be a part of my life again. This also hurts.
There is no prescription for how to deal with these losses. All I can do is leave my metaphorical door open; should there be a change of heart, there's room to reestablish the relationship.