I've talked to my sister about it a few times. She goes through many mental health struggles herself too, and she's also a very understanding person, so it can be easier to talk about these feelings with her. Although that being said, she doesn't share the same 'pro-choice' mindset that people on this site do, so there's only so far those conversations can go. But still, it can be helpful to have someone to open up to, especially when you're feeling particularly low, so long as you don't specifically mention any plans. You should really be careful about who you tell though, some people are less empathetic than others, or just aren't able to deal with those sorts of conversations!
I guess you can sort of gauge how somebody will react, based on how they talk about these things in general. My sister and I are really close, she also talks about her own struggles, and I know she has friends she listens to about these things too - so I felt pretty comfortable talking to her about this. On the other hand, my mother often talks down about mental health struggles, she has talked shit about other family members who opened up to her about them, and she generally finds those topics uncomfortable, so I have sort of learnt to not talk about these things with her!
Hopefully, if you want to talk about it with someone, there'll be somebody in your life who can be more understanding. But if not, I hope you can find comfort on sites like these, at the very least!
