I personally really struggle to talk about feelings to those who I don't have a real, genuine relationship with already. And unfortunately there aren't many people in the world who A) I have that kind of relationship with, but also B) I want to burden like that with my problems.
The likelihood is that this probably leads me to keeping a lot of my feelings "inside" and not expressing them, which ultimately probably only serves to further worsen things at times - but it's really hard to open up, as I'm sure anyone with a MH issue will recognise.