I like my best friends crush and he likes me too but she'd freak if she found out!?

hello. My best friend sense last year lets call her M, M is obsessed with this one boy lets call him J, M hardly knows j shes only talked to him a few times and has no classes with him yet she is obsessed with him and he's all she talks about I on the other hand supported her at first but Im developing feelings for him! i wish i wasn't but i can't help it he's in half of my classes and he flirts with me a lot i tried cutting off our communication so i won't get in the way of M and J but he doesn't like her like that and tbh she just met him like 2weeks ago and she moves from guy to guy really fast. I didn't tell J i was cutting off communication with him bc of M or else he'd get really mad at her, Im just ignoring him he tried talking to me and i just kept walking he and earlier had a basketball game i was there to support the basketball team he made eye contact with me more than 100 times he wasn't smiling or anything he was just looking me straight in the eye and he didn't make it in he looked at me again then just looked away and the coach had a long talk with him bc he's usually rlly good at basketball. He playfully tells me he loves me and M was beside me one day when he told me and she looked mad i can't have a talk with her or she'd just freak out last year when me and my ex were dating she very badly wanted his number and when i didnt give it to her she got mad she did the same with my friends boyfriend she tried hooking up with him. IDK WHAT TO DO I RLLY LIKE HIM?