This is a really, really hard time. You deserve much credit for staying with them and helping them through it, you are obviously a strong person. They need you. They may not tell you that, but they do. If your spouse has been diagnosed with bipolar disorder, are they on medication? How long have they been on it? When was their last visit to their psychiatrist? Perhaps it's time to take a look at their medication, maybe it's not working for them the way it should anymore. When you say that you are going about it all wrong, what do you mean? Do you mean that you feel you are somehow making it worse? Or just that you seem to not be helping?
Being suicidal shouldn't be taken lightly. Are they at home all the time alone or are they working? If the suicidal thoughts become too bad they may need to be admitted for a short time to ensure their safety.
Hang in there, it's really hard on the heart but by being there for your spouse you're helping more than you know.