When my AXH and I went through our separation and divorce it was very interesting to see which friends stuck by me and which ones went away... also which ones I chose to keep in my life and which ones I let go. It was a painful side effect of a major life changing event. It was very apparent to me that some of those life long friendships just weren't going to fit into my new existence, mainly because of lifestyles and behaviors I knew weren't healthy for me to be around. It's still not comfortable to accept that my best friend of 30+ years did not (and does not) have my best interests at heart. More names on my "love from a distance" list.
That being said, I did have to have a few heart to heart conversations explaining why I had been so distant. I had to swallow my pride and admit how far down the rabbit hole of codependency I had gone and how it had taken up ALL my energy to bite, claw and scramble my way back out of it. I apologized for a lot of things, one of which was not explaining to my friends just exactly what had been crashing and burning in my life... I could have had so much more support if only I had been honest instead of trying to keep up appearances.
Most of that was done face to face, but some was done via email as I had moved far away. I don't think it matters so much HOW you reach out, it's just important that you do. Even if some of your friends don't boomerang back, that's OK, you will know you said your piece... besides not every friendship is meant to last until the end of days anyways.
Everybody goes through rough times in life, any friend worth having will understand that.