The dude I like used to call me everyday
Now every time he calls it only for a short time
I fell like he doesn't like me anymore

Does he know that you like him? If not you should tell him.

(I answer this with personal opinion, and not in professional capacity)

So you shouldn't care I mean he used to call you he probably move on but if you miss him you probably like him try to find out and if you don't then move on also...