How do i get over an ex even though i have a new gf?

about a year ago my ex and i broke up after a year together. it was a mutual break up where she and i are still friends though even up to now it still breaks my heart that we broke up and i still cant get over her. just knowing she has a new bf kind of made me jealous as well. i recently found a new gf whom i met online and got to know her in person for a month, but for the most part it's a long dist with her. my new gf is sweet and nice, but i cant seem to fill the hole that my ex left me with even with my new gf. i know is unfair to my new gf, but what can i do to get rid of the old feelings that i have for my ex? its like there's parts of my ex that i cant forget and i cant find it in my new gf that will fill up those holes.