Ophelia, I have been following your thread from the beginning and just wanted to offer my support. You truly are having an awful time of it and, although it does not feel like it at the moment, you WILL come out stronger and better.
From what you have said it appears your DH's feelings to OW are not deep rooted. I think he has been caught up in the moment with a woman who has a lot of male attention and he has got a massive ego boast in the fact that she has "chosen" him. From what you have described it sounds like it is more lust than love. His feelings appear to be based on material things - her looks and the fact that other people "fancy" her.
I don't think this will last. The newness and thrill of it all will wear down and normalise and he is going to wake up one morning, whether that be in a day, week, month, year, and the reality will hit him like a tonne of bricks.
In relation to your house, please don't worry about this. Even though he bought the house before you were married, because you both lived in the house as a married couple it is considered by the courts as the matrimonial house and will comprise within the matrimonial property you have accumulated together during the marriage. Therefore, you have as much right to it as him.
I hope this is of some help xx