Meaning trap
fancy
be attracted to someone
To find someone romantically or physically attractive (informal, mainly British).
collocationB1common

Don't mix these meanings
Same phrase, different job.
be attracted to someone
To find someone romantically or physically attractive (informal, mainly British).
Hear it in context
Notice where the phrase sounds natural.
I think Jake fancies you — he keeps looking over here.
When I was at school, I fancied a boy in my class, but I was far too shy to tell him.
Fix the pattern
One small grammar move makes it sound right.
Not: I'm fancying her.
Say: I fancy her.
Like 'like' and 'love', this meaning isn't normally used in the continuous.