Oh I've been moved on for a couple years now. Plus M has a boyfriend and I'm not going to act like a friendzoned douche over that (especially since said boyfriend is a guy named D who I'd honestly say is kind of a "childhood friend romance" thing). Plus I never was dumped by M since we never went out and it was only ever just a one-way crush.
I don't see that as a problem. If she doesn't like you back, it shouldn't be a problem for her if you move on. While yes, it might be awkward that it's her best friend, it should be fine otherwise.
But I wouldn't ask her yet if the time she dumped you wasn't very long ago because that kinda seems like you sorta switch between them. Also, is there another person you could ask if T is single? It's a bit awkward to ask a girl if her best friend is available, you know.