correct?

Jeff became my best friend and still is to this day.

Is this sentence correct?

It looks fine to me... Why do you ask?

no,it isn't. I think it should be:Jeff became ny bestfriend and he is still now.

You're wrong Alessandra.
"ny" isn't a word. I think you mean "my".
"bestfriend" is not one word. It is "best friend", two words.
"he" can be omitted, and "now" is a synonym of "to this day".
In short, you're an idiot.