How to handle a breakup

So this guy and I have been seeing each other  for a couple weeks now, and he has brought up the topic of dating .he works for a company that does sales around the country and he had to go on a business trip ,he had me watch his dog And I told him he doesn't have to pay  me because were talking and I thought it would be something nice to do,( we have had sex)
He starts becoming a major asshole on this trip, calling me and yelling at me.
Well comes to find out he stopped somewhere with another girl and without hesitation jumped into a relationship with her, when I go to drop his dog of we get in a huge argument. 
One how I told him I have proof that I'm always  number 2 ( guys always pick other girls over me  its my number 2 theory)
And how he could've just told me but I was acting crazy and I shouldn't have feelings because "we were just friends ".
So now I'm sitting in my gym parking lot  baling my eyes out with my Bestfriend, 
He made me believe that I was the girl he chose but obviously waiting till I'm 18 was way to long (3 months)
Am I the crazy one?