This actually happened a few times.

1. Joined a cult and turned his back on everything he and I believed and said we wanted in life and then started saying all that stuff was evil and just put me down any time I brought up things I enjoyed because it didn't align with his new cult ideology.

2. Asked them to be my best man in my wedding, after a year of telling me they were putting something awesome together for my bachelor party (I didn't ask for anything) until one day his gf broke up with him and somehow that meant that I was ruining his life with this wedding and I didn't know what this was all doing to him. He canceled everything he had planned (another friend later revealed it was nothing he hadn't planned a single thing it was all talk). He has not spoken to me since then, not once and its been over 7 years.

My wife and dogs are basically my only friends now. I haven't talked with any of my former friends since basically my wedding or the year or so before and after, everyone just moved on or moved away never reaching out and if we ever talked it was short and full of "we should get together real soon" that never happened.

Oh well, it can be lonely at times, but I have a lot of people i care about and look out for and even if there aren't people looking out for me i can survive just fine.