<human>: Could you distill the essence of the text into 1-3 sentences?

Typing from a cell phone with a broken screen, sorry for any typos.

My bestfriend and his fiancee recently broke up. There was constant fighting between the two of them over the past 6 months where I tried to be of help to them both. I never picked a side, but it became very clear that he was emotionally abusing her. After their last fight before the breakup, I told them both that I would not be supporting their relationship any longer.

Now that things are over between them, it appears she has gone no contact. He has gone very public with it on Facebook, saying how he doesn't understand what happened and creating lies to make people think he is innocent. This has really been bothering me but I haven't dared to say anything to him in fear that he'll get upset with me.

Just yesterday he has started prying me with questions about if and what his ex and I have been talking about. I told him the truth (the ex and I have talked about half a dozen times, once about their relationship in particular and how shitty breakups can be), which I am starting to regret. He continued to ask me questions and I stopped the conversation telling him that he knows a whole lot more than I do on the situation.

Today my bestfriend has messaged me twice and I have not replied. First he asked me if his ex was online, then if I could forward a message to her (no idea what he wants me to say as I haven't gone into the messenger app to mark them as read for him to see). I do not want to be his messenger or spy, this makes me feel extremely awkward.

How can I politely tell him to back off. I usually react to things like this in a negative way but I don't want to upset him. Over the past month I have also been feeling a lot of resentment towards him over his actions during/after the relationship and have a hard time spending time with him. Am I over reacting?
<bot>: Bestfriend is trying to get me to talk to his ex-fiancee for him. How do I tell him politely that I am uncomfortable doing so and stop asking awkward questions.