Did you try antidepressants already ? This worked for me and helped me to combat my depression, combat my melancholy and significantly increase my motivation. In particular, the more modern SSRI and SNRI antidepressants, that are nowadays usually prescribed can (proven) increase suicidal behavior, especially at the beginning of treatment. Could be something for you. Are you in treatment somewhere? c:
Is alcohol perhaps an option ? I need alcohol to deal with the guilt I feel towards my family and friends, and to plan exactly when, where and how I do it. Will need drugs or alc too when writing my farewell letter. Didn't began yet unfortunately...

Btw. one can be suicidal without beeing depressed - think about it.