How long have you been married and do you have dc - if so, how old are they?
Are the problems you're experiencing in your relationship due to his abuse of, or indifference to, you? Are there 'communication' problems? Is he, or you for that matter, a selfish, inconsiderate arse? Do you think he's having an affair? Have you met someone else?
Is there any particular reason why you are considering separation rather than divorce?
Whatever the difficulties or issues may be, would you consider joint counselling at Relate or similar in order minimise fall out if you split up or to see if you can revive what may be dead in the water?
As you can see from the above, if you don't give any info you'll be asked a lot of questions, many of which may not apply to your situation.
To get your story out, start at the beginning - you may find it cathartic.