Yes I suspected you might be. I really think you should deal with that first since it's very hard to have any feelings for people when you're worn out. And when I say 'deal with that' I don't mean medicate yourself, I mean what I said above - change something (if that's at all possible). I think you're having a very normal, sane response to the situation you're in (3 children under 5, and whatever else life is throwing at you right now) so I don't mean stop being depressed, I just mean stop - say yeah this phase of my life is pretty bloody hard going. What can I do to ease things up a bit? Just sort of take stock. Go easy on yourself - give yourself a break, give your partner a break (I mean gimme a break, not take a break from life - although of course if you can find time/money to 'have a break' then that would be a no-brainer too), give your relationship a break. Just find ways to live through this phase as peacefully and consciously as possible.
As I said above, getting some space would be my advice.
This is rather rambly - I'm a single parent to 3 small children and was up a gazillion times in the night with my littlest one and am zombified today! I endured the divorce with 3 under 6 route and seriously would recommend trying all other options before you head down my path. XX