How do you do it?

I was sexually abused as a child and in my last marriage. Lately I have been unable to make love to my husband. The flash backs are so bad, even when I think about it. My husband wants a seperation because of this. He has'nt done anything wrong. I guess he just can't live without it. I just can't take myself to a place where I know I am going to have flashbacks. What do I do

You have to slowly 'sneak' up on the desired behavior. Determine what you ARE able to be comfortable with, It may be holding hands. SLOWLY move toward more intimate behavior. Maybe a foot or back massage and so on.
When you start to feel uncomfortable, back off and think of something pleasant to stop the discomfort. Keep trying to move forward from new comfortable behaviors but not more than you can enjoy. In time you'll probably work through the earlier inhibitions unless you somehow think that you 'shouldn't' engage in these behaviors. That is a different problem.
Good Luck
Michael