Dear J. maria,
God bless you as you ponder this question.
I was always taught by the many priests I have known (they all seemed to be in agreement) that of course, the mentally ill and disadvantaged are very close to God's heart and they carry a special cross that the rest of us cannot understand in this life. I was always taught that these people are very precious to our Lord and they sort of fall into that category of "little ones" that Jesus talked about. They are defenseless and therefore our Lord cares for them in a special way.
RE: those who commit suicide or are in danger of this: I have always been taught, and I firmly believe, that there is no darkness our Lord cannot breach, no place in the Universe He cannot go, no illness he cannot cure, no death He cannot overcome. Our Lord overcame death --- those who have fallen prey to the evil one through suicide, now and in the past or in the future, will be touched and met by our Lord in some way, some how, and in whatever way is possible. Those who have committed suicide, are those who have indeed been harmed/hurt/afflicted by the evil one, whom our Lord said, "is a murderer from the beginning." I believe our Lord has a special plan for these unfortunate souls and He will right all wrongs, He will heal all wounds, He will bring them to a spiritually healthy place where they can communicate their troubles to Him directly. We must pray and hope for the salvation of ALL people.