YOU SAID:

My best friend is dating my crush and she knew he was my crush and still dated him

INTO JAPANESE

私の親友は私の好きな人と付き合っていますが、彼女は彼が私の好きな人であることを知っていて、それでも彼と付き合っていました

BACK INTO ENGLISH

My best friend is dating someone I like but she knew he was my favorite and still dated him

INTO JAPANESE

私の親友は私が好きな人と付き合っていますが、彼女は彼が私のお気に入りであることを知っていて、それでも彼と付き合っていました

BACK INTO ENGLISH

My best friend is dating someone I like but she knew he was my favorite and still dated him