I think Outlaw summed it up nicely. Your son is aware of your difficulties, even at very young ages kids pick up on these negative vibes from their parents. Often they misinterpret the situation as their fault.
My parents were "incompatable" to put it mildly.. all four of their children heaved a big sigh of relief when they finally seperated. I had migraines as a teenager from the tension at home.. you could cut it with a knife. They didn't have to argue in front of us for us to know what was going on.
Whatever choice you make I ask that you consider this: Please do not ask your son. Do not sit him down and explain that mommy is unhappy and thinking about leaving daddy and what does he think... Present him with the desicion when you have made it, not while you are deciding. I suffered years of mom asking what I would do if she left dad, or what I thought about us kids and her moving into our own place. I love my father and my mother.. I felt like I was betraying dad if I agreed we should leave and I was letting mom down if I said we should stay.. there was no right answer from my perspective, even though I knew everyone would be happier if they were seperated.
My youngest sister and I discussed this recently. When she was the last child living with mom and dad she was repeatedly told by mom that this time they were leaving for sure.. One time mom had gone through her entire speil without much response from sis.. she asked her what was wrong and my sister said I don't believe you.. The next time mom brought it up it was to tell her to pack what she wanted to take they were leaving tomorrow. My sister said yeah ok and didn't pack anything.. so she was surprised the next day when mom's friend showed up to help them move out.
It's totally unfair to your child to put any part of the burden of this desicion on their shoulders. Or to treat them like a confidant, they are not your shoulder to cry on, find an adult.
Ok, I got my little rant out :)
As far as living as roomates goes... this may be fine for awhile, a transitory period, but for the long term you might want to think about other possibilities. My ex-husband was raised my parents who lived like roomates (right down to seperate bedrooms) He didn't have a clue as to how to treat his wife (me) like a wife, so he treated me like a roomate. (ugh) Course... he was also gay, which may have factored into that..... sigh, if only I had known... but that's a whole other thread.
Misty