Yes, there are missing facts. I think John did like, unlike, and relike some photos and I believe this made the accuser uncomfortable. My opinion about the wise course of action after that is as follows:
A private confrontation undertaken with a moderated emotional tone.
If that does not work, and said person, after having been appropriately blocked, still finds ways of harassing you, contact the spouse and express your concern.
I still haven't reached the point of taking this to a public venue.
The spouse gets short with you and accuses you of being the problem. The problem does not stop and you are being harassed.
Contact Facebook. Law enforcement.
At some point, if the problem continues, you will likely lose it and start fighting back on the person's social media platforms.
And at that point, I would say the stalker probably had it coming.