It would be really great if the choice not to use Facebook did not often entail serious negative consequences. For one thing, I'd be a lot less annoying on the subject. Unfortunately, that happy state of affairs does not appear to obtain in either case.
You don't know if it was "opting not to use Facebook" that lead to decline in your social life, because you didn't test whether "being on Facebook" would not have lead to decline in your social life.
(I've seen many articles that state exactly the opposite - that people who have less social interactions spent more time on Facebook.)
https://news.ycombinator.com/item?id=12009198
https://news.ycombinator.com/item?id=12362818
(Maybe it's necessary to point out that I'm aware of the possibility that all the apologies I ever received on this subject were lies. I'm aware of the possibility that all the apologies I ever received on this subject were lies. Given that no evidence exists to support that conclusion, parsimony would require it be disregarded even were I otherwise inclined to imagine that all my friends actually hated me and didn't want me around, and were willing and able to deceive me by presenting the impression of sincere regret for having forgotten to include me.)
I'm still working on a better metaphor than that of an abusive relationship; while that one speaks strongly to me, my experience suggests it does not do so to others, which renders it useless for my purposes. Any suggestions you might have to offer on a more effective replacement would be welcome.