Oh Tori, I feel for you I really do. There are brilliant posters on here who will come along soon I'm sure with their brilliant wise words and advice that help so much.
Meanwhile, I am confident enough to tell you the following. With regard to the emails, be completely business like. If it helps, imagine that these emails will be read publicly. Just stick to the facts. Do not put anything in them that is in any way emotional. These are now financial negotiations only. It is important to make an appointment with a solicitor as soon as possible too. This does actually help emotionally as you will feel more secure as a result.
I cant really comment on your dd as my youngest was older than her and it does make a difference. If she is not asking to see him it may be sensible not to do anything about access at the moment whilst you both get over the shock. You can support each other.
Do not look for reasons why he left. Any he gives you will be hurtful and quite likely lies in order to justify himself and his actions. Now is the time to put a practical hat on in any dealings with him, and rant away on here or to friends in RL.
As for the light at the end of the tunnel, I wont tell you it is easily seen because it isnt. There will be days of light and days of dark but just take one at a time. Be very nice to yourself and your dd. Do nice things, have treats, book the hairdressers or a massage. Promise yourself on a bad day this is only today and tomorrow will be better, because it will. You will find the strength to get through it but it is the terrible shock at this stage which is so hard. Once this bit is over, you will be surprised how well you manage. Deep breaths. Keep talking, keep posting.