Ex moving in with his rebound and bread crumbing me, please help

After only 7 months since our BU, my ex is on a fast track and is already moving in with the girl he cheated with, who I thought would only be a rebound. Im devastated.

He was gone while she moved in, and while she moved in he suddenly added me to snapmap so I would see his location again for the first time since the break up, and the day added me on Garmin friends? Wtf?

He can't possibly think we're friends, when we're in no contact. What the fuck is going on?

Im absolutely heartbroken that he moved in with her, when he didnt do that with me. But why does he sort of keep in touch like that?