I am not admitted in Michigan.  You are still legally married, correct?  There is no formal separation agreement, correct? The question becomes: is the house marital property or not? 

There are many ways to hold title to land and it may or may not matter here how it is held.   Let's say here that he bought it after he left and with the girlfriend they hold it as tenants with rights of survivorship.  If it is held that way then by law it passes to her upon his death.  If they hold it as joint tenants without a right of survivorship then half of the house is included in his estate.  He may have bank accounts with her as well and if they have a POD (payable on death)form she would get them too.  Otherwise, only half of the money is considered hers.

What I really think is that you have a valid claim to elect against his estate but that you need to see a lawyer in your area who can get all the facts and time line down.  You may have to sue to have a judge make a determination that assets are "marital assets."  Good luck. 

The answer depends upon the deed to the house.  In general, if the deed is in his sole name, the estate assets pass to the wife.  There are exceptions and it also depends upon the value of the estate and whether there were children to the marriage.  There are also claims against the estate that only a wife is entitled.  Please contact me to discuss in further detail.  586-868-5100, John R. Tatone, Esq.