I want to install a single pole dimmer. When I opened the switch on the
wall, I discovered 3 way wiring. Apparently, this switch was intended
to work with another in the room.

I din't want that. I want the dimmer for this single light only. When I
disconnected 2 of the black wires (they were joined together with a
murette) the other light went off.

How do I connect the single pole to the 3 way wiring?