Why on earth would you buy a house with a man who is still married to someone else?

Your post implies that he hasn't even filed for divorce yet. But, according to you, they have been apart for almost a year. Divorce can be expensive, but so could him buying a house while he is still married to someone else. It's called marital property. While a judge may eventually rule that it isn't, a judge may also rule that it is marital property since the divorce hasn't been filed.

And the fight over the house will make the divorce even more expensive.