Ye. Two and a half years ago now? Fairly sudden, but - in hindsight - not necessarily unexpected.
I didn't really properly start dealing with it until about a year later, I think. There was too much else going on before that just took all my attention and that I really couldn't avoid dealing with, no matter what - and when that came around it was less in a 'oh god she is gone' way but more in that, I do really miss her type thing.
As SimonG I am not all that sentimental about death, really, and it wasn't the first time someone I was close pretty suddenly and unexpected died (had one of those every decade, fairly much, so far).
To the OP: Most important thing is, really, to go and look for someone to talk to. Online works, but much better if it's out there in real life. Get it out of your system. Do consider and go for counselling if you need it; if there's one thing that really can help with it is the griefing process; especially with suicide involved.
Regarding these:
EC-: Is it something that still affects you? How do you feel now about the person, and their choice? Did you know that they were coming to the decision? If so, did you say anything to them (and if so, what)?
First of all: Without knowing you / seeing & hearing you say this but because of what happened I just have to ask: Are
you feeling suicidal? I know this is an interpretation around several bends, but better asked than not.
Anyway. Does it still affect me. Yes. Not in a major disruptive way, but I am aware it happened. I am writing a novel that somewhat touches on this; it's not about her directly though - none of the characters directly resemble her (or me) - but yes, that there is a suicide in there comes from somewhere.
I didn't know she was coming to that decision but it was such a complicated case - including some utterly major mess up of clinic staff - that it is really clear this was what she wanted at that point and very little would have stopped her. (There were five attempts in a really short time scale; she was sectioned and then, the same day, released into somebody's care which A] just shouldn't have happened and B] was the worst person to deal with this possible; the sixth attempt was successful.) I don't think anyone could have prevented her from trying and trying again at that point. No matter what I - or anyone else - had said. It was still her choice to do this; and her choice not to seek out help earlier.
I didn't speak to her, not about that. I left on holidays, then came back, and left for a music festival straight away. Her flatmate called me on the way there and told me what had happened; couldn't leave until the festival was over, as it was in the middle of nowhere. The last conversation I had was before my holiday asking her if she'd look after my plants in case my flatmate would have to leave town, too. She said she would. I didn't notice anything telling in her behaviour at that point.
EC-: What would you tell someone else thinking of suicide?
Regarding that one and having been on both sides - I have had my own mental ill-health past (from depression to self-harm, to suicide attempts): Take it serious, always. Don't react emotionally - it's a lot for somebody to come out with saying that's that how they feel. It takes a lot of trust and requires overcoming a lot anxiety for somebody to state that openly - one of the biggest fears, usually, is that it's not taken seriously; that somebody dismisses them or reacts in a judgemental/aggressive/unfair way. Usually people choose and think about who they open up to, like that, very carefully.
So just simply do accept that that's how they feel, don't make a big deal out of it, but stress that they need to seek help. Accompany them. Be around and stick around. But always keep in mind that they are making the decisions in the end. That's the case with anything relating to mental ill-health. You can't make somebody better, but you can help create the right setting for them to get better. Much as no-one can heal somebody else's physical health; even doctor's only assist the healing process.