Should I pursue him...?

There's this guy I go to school with, and we're really cool...we even hang out after sometimes..with friends, and a few times alone...So, sometimes he tells me how beautiful I am, and how he thinks about me all the time..he calls me when he is at work..he gets almost mad or offended when I dont return his calls...but then there are other times where he talks about his ex all the time, and how much he misses her, and also talks about other females ...so i guess what I want to know is if i should take him seriously, or just keep our friendship platonic?