I think that Geoff has given you some good advice, in other words to write things down - taking your time to do so, then handing over the paper to the councilor. I've done this with doctors and have found it very helpful (so have they as they have something to work from)
I get to say everything without being flustered or embarrassed by trying to explain face to face, in fact I've just has to answer questions to amplify what I wrote (which I've normally written point-form)
I'm not sure how much you have to say to your year adviser to get an appointment with a counselor. Simply saying it is a serious and troubling ongoing matter - without going into details may well be enough.
When you see the counselor you simply had over your situation in point-form (well, I have used point form anyway).
Everyone is different, I used this method not only to make the consultation easier for me, but also so I did not chicken out on some things - too late when the paper has been handed over, which was a surprising relief.
If you simply can't say everything all at once then just say there is more, but you can't talk about it -and say why. That way the councilor will know it is serious and needs to keep on going.
When you do it? I guess when you think there is a good opportunity, hopefully as soon as possible, not leaving it until next term as your life needs to get better right now. I left things far too long and had more difficulties as a result, please don't make my mistake.
Do you think this is something you might be able to do?