'friend' sent me this message, pls advise

So this guy S used to work with my roommate M, before he was fired for having a shitty attitude. M is all about shiny-happy nonjudgemental hippie love, so even though S was acting like a dick to most people, M stayed friends with him because she was sure there was a good person deep down. I think she's right, and C (my other roommate) agreed. As we collectively peeled away the layers of S's defensive mechanism of acting like a bigoted hypermasculine superdick, we did indeed reveal an absolute sweetheart underneath the hard outer shell.

Recently, S told me he was pissed off with C because he found out that she was getting back in touch with her abusive ex-boyfriend. S told me he was fed up with C's self-sabotaging behaviour in this area, which I understood, although I still do want to support/sympathise with C rather than just abandoning her because she's having a hard time cutting off her abusive ex completely.

A few days ago I saw that S had sent me a facebook message, and the preview was 'You'd be interested to know just how she feels about both of you.' I'm fucking sick of grown-ass adults playing the Mean Girls game, and have major anxiety issues around Potentially Bad Messages on the Internet, so I didn't open the message for nearly a week; to be completely honest, I only read it last night because I got drunk first. I knew I wouldn't be able to convince myself to read it otherwise.

This it what S's message said:

I've been rehearsing potential responses ever since I saw the message preview. Before I had read the full message, I was expecting that my reply would be along the lines of "Honestly, S, I don't want to know. If [whoever he was talking about] has a problem with me, I'm not gonna deal with it unless she says it to my face. If one of my roommates doesn't like me, I honestly don't care unless she confronts me to say she doesn't want to live with me any more. And if [whoever it was] has something shitty to say about me, I'm not interested in hearing it from you; I really don't want to know."

I know I ought to respond to S now, and I want to make it clear that I still value him as a friend, despite all this drama. But I also want to make my above sentiments clear - that I really don't want to get involved in Mean Girls bullshit, and that I do not want to engage with this kind of crap. I think that maybe the best way to respond would be to just not reply, which I've already been doing for over a week, but S has done a lot for me and I don't want to just stop speaking to him entirely... what do you guys think?

(posting this partly for input, partly cause I just need to talk about it somewhere)