I like my ex that is my best friend thats dating another girl?

ive dated a guy for 2 and half year and we decided to be friends after we broke up and we were friends with benefits ive only dated him and now ive known him bit more then 3 years and he is dating another girl it was so surprising it completely took my breath away in a bad way ofc. and he always flirts bit with me tells me that he loves me so much and doesnt want me to leave him and sometimes we cuddle but not any longer i dont understand why because he is always saying that he doesnt like her that much wondering if he's lying to me so he can hold on to me. i loove him soo much and i know some ppl will suggest stop talking to him but he's my best and kinda my only friend that i tell everything but i know im major depressed because of him please help me :C