feeling You may be miles away, but it's still possible to have an emotional affair.
He told you to ignore his wife's request. So, in essence, he is trying/wants to deceive her. Otherwise, what would be wrong with you being friends with her?
He wants to keep you separate.
If you have feelings for him, then unless you confessed them to his wife, any contact would be deceitful.
This kind of relationship is more dangerous, as it never really had closure. In a way it's easy to romanticise it - 'star-crossed/fated lovers' - and whilst you both harbour feelings for each other, then it can never be a truly platonic friendship. There will always be a 'what if?' there, and that is harmful to his marriage.
I know it's hard, but yes, you need to block him from Facebook, and also block his number on your phone.
It will get easier, and you can get on with life. Find someone, who is able to give themselves to you fully x