Is it wrong to still be in love with your ex while being in a relationship?

I have a boyfriend i seriously like him alot but my love for my ex is still here i dont know what to do it seems like everytime i get in another relationship with someone else i reminisce about him more and thats what cause breakups with my relationship with my boyfriend im basically torn i wanna move on but i cant my ex has a girlfriend but seems like i cant move on myself and really wanna