Crush Advice!!! (help)

So I have a crush on this kid let’s call him J. So basically I’m pretty sure J like me all his friends always tease him when I’m nearby, I always catch him staring at me, and and couple months ago at a dance his friends told me he wanted to dance with me and I said no ( the rest of the dance he looked really sad ) So we don’t talk but I want to I just don’t know how to do what should I do??

Also his ex and me are okay friends she doesn’t know I like him and I feel like if she did she would hate me because she knows he like me and always tells me how she feels bad for me (she hates him for no reason) so what do I do about that???

PLZZZZZ HELLLPPPP