More thank a crush?

I've liked this boy for 4 years now, I've heard that if you like them for more than 4 months, it's more than a crush. The thing is, I've recently found out that he likes my best friend (even though he has a gf). He only sees us as close friends.

But what I don't get is that he can talk to me more about personal things than he can to his girlfriend?

I'm confused and frustrated rn. I don't know what to do....