It's good that you realize the problem is your thinking. First, tell yourself NOT NOW. If you have to, you can always keep that final option, but there's no reason to do anything right now.

Next, don't feed your thoughts in this negative area.
Distract yourself with something that keeps you from thinking about anything dark. Even mindless computer games are better than wallowing in that dark spiral which only drags you further.

Remember, depression tells you lies. You do not want to make ANY important decisions when hearing lies, right?

Do thought blocking whenever the topic comes into your mind.
You haven't always felt this bad, and you will feel better before long again.
hang tight.