my best friend is dating my crush

im in high school and have 3 classes with my friend and 2 with my crush. my crush texted me and said he liked me and wanted to get to know me. but the next day my best friend asked him out and he said yes he never told me he had a gf so now my best friend is accusing him of cheating with me. i really like this guy but i know that i cant date him even after they break up because you cant date your best friends ex.