I cant get over him :|?

i thought i was over this guy who i was with for 5 years. Im with another guy its been 6 months. but the first guy , why do i get jealous when he talks to other girls? hes hurt me so many times but still everytime he tells me he still loves me i foolishly fall more in love with him :| the new guy im with is really nice and i know i love him but then why do i miss my ex so much?! what should i do advise please.?