D and I were phenomenally good friends, the sort you are lucky to have once in a lifetime, and the sort you hope will remain connected with forever. Most of our mutual friends didn't believe that we weren't sleeping together, but we were true Platonic friends. We were good for each other and got real joy out of our friendship. He was Jewish but knew nothing of Judaism.
At that time I was still living at home, and D came to us many times for dinner on Friday nights; candles, kiddush, everything...our normal family Kabbalat Shabbat. I think it absolutely blew him away how Yiddishkeit could be something ordinary that you just live and breathe and it is part of you. That got him interested in exploring Judaism for himself.
He took a sabbatical to go to Aish Hatorah yeshiva in Jerusalem, and basically never came back. We corresponded, and when he came to England to visit his parents we met up. Within 18 months of going to Aish, my dear friend would no longer make any physical contact with me, not even to shake my hand, and would not look me in the face when we were talking...not that it made much difference any more, because there was nothing for us to talk about, we no longer had anything in common. He was a different person, utterly uninterested in the world that I still lived in. The last I heard from him was when he wrote to tell me that he had a shidduch and was getting married.
He was a 'seeker' IYSWIM, looking for some meaning in life, involved in Friends of the Earth, an engineer who chose to work in the field of renewable energy. I suppose I'm glad that he found the meaning of his life that he was looking for, but I feel that he also cut himself off from his life in the process.
All my family on my mother's side are Hassidic, and I never felt cut out from their lives as I have from D's.
I heard somewhere that Chozerim BeTshuvah who go 'the whole way' generally remain ultra-ultra-orthodox for 2-5 years, and then start picking up bits of their earlier lives again. I still hope to hear from D even though he hasn't ever answered any of my letters since he told me he was getting married. I suppose he must have moved around, so addresses are out-of-date. I haven't written to him in years now.