l've been following this post, @MarthasGinYard, and l feel for all of you of you.
lt looks to me that he's the kind of person who can compartmentalise things. My ex used to do that. Whatever's going on, they can put it in a mental box and carry on as normal, or near normal.
l may be wrong, but it also seems to me that maybe he has a hidden agenda and he's using this as an excuse to split up. Maybe you shouldn't have snooped, but this seems a huge over-reaction. l can understand it causing a row and maybe a few days of being pissed off, but seriously, after 12 years, unless there's another back story here that you haven't told us about, it seems very odd.
Of course everyone has problems in their relationships (especially long term ones like yours, that's human beings for you) but him saying he's "looking forward to being on his own", assuming he means permanently, just doesn't ring true with me. Either he's been very unhappy for a very long time, or he's got something or someone else going on.
l'm afraid l don't have any answers. Take things an hour at a time, and don't make plans besides getting things in order and looking after yourself and your daughter. lf he's choosing to be arsey with you in front of your daughter, that's not on - none of this is her fault, and he should be a decent dad and keep things as civil and normal as possible when she's there.
Go on your holiday with the little one and take a friend (even for a day or two if you can). Try to focus on her and your time together, and don't even think of suggesting you split the time with him. lf he wants to take (what he considers to be) your 'unreasonable' behaviour out on your child, albeit indirectly, that's down to him - how he chooses to behave is entirely down to him.
Get legal advice, get your affairs and finances in order, and above all - please, do not discuss it with him. lf you have to share the house with him til things are sorted out, do it. lt isn't easy (l've done it) but you have as much right (with your daughter) as he has to live there - don't let him coerce you into leaving. He also has the right to be there, but he needs to appreciate that his problem is with you, and it should affect your child as little as possible until things are resolved.
l wish you well, l know this is very difficult and things seem very confused and bleak just now. But things will get better with time, and the main thing is that your child knows that her parents love her. x