The internet is not a great place for a marriage. I'm happy that your DH did the right thing. IMO......harmless flirting is how it all begins.
The internet isn't agreat place for untrustworthy spouses, or rocky marriages. Its a fine place for the rest of them.
I'm not sure that him deactivating the account really means anything - least of all that he's doing the right thing. I know that he has exchanged email addresses with at least some of these women. So it is certainly possible that he could continue his relationship with some of these women - only this time, where I can't see what is being said.
Also, being new to Facebook, I don't know if it's possible for him to go back in a create a new account that I don't know about. I would think so tho - as long as he is careful about what name he uses and who he friends.
I probably sound paranoid but, yes, we have had some trust issues in the past. I have very good reason to be suspicious. I thought we had come a long way but apparently not.
What your dh did wouldn't bother me if it was my dh, I don't care about harmless flirting. I may razz him about it, but it wouldn't upset me.
However in your marriage it doesn't seem like its harmless, and since you have past issues you have every right to be upset.
ETA do you have kids that are on FB? I think if my kid's saw their father say that stuff I'd be upset. So I guess in a way I do think its inappropriate.

The Dis should set up a board just for therapy sessions.
It has actually helped to hear from people who see both sides of this.