To be honest mate it seems like this was brewing for a while. I know it might not be what you want to hear but by the way you put it, it sounds like you have a bit of a short fuse and by having the hump quite alot of the time may have been they key to her doing the off! In my eyes if you're arguing all the time then your obviously not really a good match! But if she can just do one without a word or warning she's a pretty hard person and it probably best she's done it now and not when you had a kid! I know it's a kick in the balls but ride it out and wait for her to explain why, but I have found that 9 times out of 10 once people seperate and move out, if they do get back together it doesn't work cos the trust has gone and is always eating away at the relationship

Sorry for all the doom and gloom but it sounds like the best thing for the both of you, but it is just my personal opinion!

Ps get the RSPCA on the case of her folks - cruel c##ts!