Why is my mom making me choose sides?

My mom and dad used to argue allot when i was little i used to think that my dad was some kind of devil they broke up about 3 years ago and its was just my mom my older brother . I started hanging out with my dad and hes not that bad a guy i thought he was but mom keeps getting jealous so everytime i go hang out with him when i come home she always makes it seem like he was just using me and she swears hes so desperate for her n stuff, i just brushed it off and thought nothing of it but after a while dad started tellin me to tell ma that he loved her n stuff like that so i fell like Im being used in a way but at the same time i feel bad for my dad like i feel sorry for him cause he always talks about how much he loves her n stuff. so he called me one day and he asks me how ma was and i was like "shes just as crazy as ever" and laughed and ma overheard and she was cryin about it. And was like I dont need to live with her and wants me to completely stop talkin to dad.