Thanks for sharing this. I'm sorry you lost such a good friend. But I'm glad your heart is healing even if ever so gradually. I can't say I've ever had this kind of experience. I never had many friends to begin with. And the few I had never achieved this kind of depth. As a result there's probably not a lot of advice I can offer.

My own go-to practice for this kind of heartache is the practice of compassionate abiding. Perhaps you're familiar with it? I simply welcome the thought, breathe into it, & smile to it. I may even place a hand over my heart as a sign of lovingkindness & compassion for it. Then, after a few moments, I let go of the thought itself & simply continue to breathe into whatever emotion lies below the thought be it sadness, fear, regret (or even joy!) It is a Buddhist practice I learned from reading the books of the Buddhist nun Pema Chödrön. May it be of benefit.