I have just had to re-read all this thread again - my heart goes out to you Viv and what you are going through.
Lots of people have written lots of constructive comments and I thought I would just add mine.
He has finished his affair and now decided he wants to come home but that really isn't his choice - that is a decision for you to make and for you to decide whether you can ever forgive him. The reason I ask this is because my husband left me after I had an affair and, after 2 years of trying to make the marriage work and having a third baby, he then decided he could never forgive me, told me we were over in February and actually moved out 3 weeks ago.
When I think back over the bad times we went through (and, boy, were some of them really bad - horrible nasty things being said), I used to imagine what it would be like if he turned round and told me he wanted to give our marriage another go, although this never happened. I am now over this and know we are never going to get back together again and am now having a good life although I still see him when he has the children.
What hurt me the most was that he has a girlfriend and they say that when you can't have something (in my case, my husband), you want it even more and that is so true.
What I am trying to say is that I have analysed my feelings for him over and over again (although obviously my circumstances are different to yours in that it was I that cheated and not him). I always thought we would grow old together but when I actually started analysing how I felt about him (although it was him that ultimately finished our marriage), I decided that I would have rather been with him than without him as the thought of being on my own with 3 children was so daunting but that is not enough reason to stay together.
When I thought even deeper, I knew that we had not been making each other happy for a long time and, at least by separating, at least we might each have a happy life, although my children might not agree with this.
Sometimes it is easier to stick with what you have rather than have to face the world starting afresh (although I didn't actually have that choice).
I think your husband might be acting the way he is towards you is because he also feels so guilty at what he has done to you and what you are now going through. Perhaps it is easier for him to distance himself from you to ease your own guilt.
You need to discuss all of this with him and you both have to communicate with each other about what you are going through. These issues, however much they hurt, are going to have to be dealt with if there is any chance of you both moving on in your marriage together.
You say the affair was with your best friend - do you still see her around? Was she married or in a relationship? How do you feel towards her?
Do you think you can ever trust your husband again because, without trust, there can be no relationship. What happens if he wants to go out with the lads for a drink (if that is what he does), will you be wondering what he is really up to.
He has got to prove his love for you and prove that it is you he wants to be with - not just for the sake of your DD but because of you.
I am sure I have not been much help and have just been waffling on, but just to let you know I am thinking of you and hope you can both get through this.