Woah... this is quite insightful, especially dmpoole's post.
That's one thing that's been an issue (I say issue, it's more of a lack of understanding on my part) in my relationship with my Girlfriend (soon to be 2nd year). She suffers from OCD and it was triggered on 04th July 2007. Just came out of the blue after a situation arisen from her little sister breaking her trust (long story).
Since her OCD, she's been depressed, because of it and her outlook on life is very negative. She has been on counselling sessions, been put on a low dose medication which she voluntarily took herself off it as after 3 months, she felt more depressed by taking meds.
Although she's claimed she never felt suicidal to her counsellor, she has confided to me that there were occasions where she feels like jumping in front of the bus that's travelling down whilst she is waiting at the crossing, but never took the step as she considers it an easy way out and it's unfair to her family, friends and I.
It is very weird seeing how she can swing her mood from an ecstasy high to a depressed low numb or angry, phobic mood. Anything that can trigger her OCD will mark the start of the rollercoaster ride, for her and anyone standing next to her.
I know it's very hard for her but it's also very painful to be the one next to her, knowing it's so hard and feeling helpless to her suffering.