Sorry to hear you had to go through that. Although I am male and I cannot fully relate, given your position and your belief that you won't face career repercussions, I'd perhaps do one of the two following things:

I) Ignore the messages and try to downplay the role of such past advisor in the acknowledgements of your merits, or II) Reply positively to the message request, start a conversation and wait for him to make a mistake. I'm not sure but I believe Facebook messages might be enough for you to prove his behavior and make him face consequences. If not, play cool and the next time you meet the guy in private record the conversation - if he does it again, you'll have proof that can put an end to the abuse he might have been enforcing upon who knows how many people.

The second option is what I would do, probably, as I cannot really stand people in academia who take advantage of their power position and abuse others. But be safe! Good luck!