If I am legally married but have been separated for 10 years and want to buy a house, what do I do?

Divorce him.In Nevada "the community" continues until the divorce. Accordingly, he is still entitled to 1/2 of everything you have accumulated the last 10 years including the equity in the house you are purchasing.

You need to divorce him. That means filing for divorce and serve him by publication. I suggest you hire an attorney to get it done promptly. And who knows, maybe he is dead.

Although you are technically separated and having seen him in so long, you are still "married" and he would gain certain legal interests/rights in any new property you purchase EVEN IF he is not listed on the new deed or mortgage. For this reason, the Lender is correct that something more needs to be done, but it is not the case that the only option is that he physically has to attend your closing. When you know where the person is AND they are amicable, you could simply get a separation agreement drawn up, or even a shorter, simpler document called a Free Trader both parties waive any interests in new property either acquires from now until divorce. But if he is not amicable and/or you cant locate him, then you do need to move forward with filing a divorce and it sounds like you will have to serve by publication in the newspaper, which is not typically something you should do without attorney assistance to make sure it is done correctly. If your closing is anytime soon, that will be a problem because it usually takes at least 45-60 days in most counties and longer if you have to do publication. You should consult with an attorney.

The title company is right. You need some kind of court order to allow you to finish your purchase. You will need the help of a lawyer so don't delay.

You will need to file for divorce or legal separation and make an attempt to locate him. If you cannot locate him, the court may allow you to give notice by publication in the newspaper. I would recommend working with an attorney for this since you'll have to prove to the court that you have made diligent efforts to locate him.