Grief is a very powerful emotion
and you can have both
grief and depression at the same time.
Grief and depression are like brother
and sister, if you will, and both can cause you to have feelings of suicide etc.
So, what you need to do is get in to talk to someone who knows about both grief and bipolar. You need to move through this process of grieving and take care of yourself and your girlfriend. You can do this together, and support each other.
I am so very sorry about your loss.