My future ex wants me to take a house after divorce .We have a house in Las Vegas, how to make sure that after a divorce a house will be only mine ?

Your facts are a bit unclear.  Presuming the house is jointly titled (or in his name) now, the Joint Petition, AND the Decree, should clearly identify the property in quetion and recite on the face of the documents that it is to be your sole and separate property.  Then make sure yoiu get a deed (Grant, Bargain, and Sale, or at least Quit Claim) that he signs, clearly signing over the proeprty to you -- and do it promptly; last year the Nevada Supreme Court said that if you wait too long to do the paperwork, property transfers are abandoned under the statute of frauds. You can do all this by joint petition, and at a bare minimum you should review the rules for how property and alimony work in Nevada, which you can review here and here.  Other information is posted at the self-help center, which youi can reach here.  But your best bet would be a consultation with a qualified family law specialist to lmake sure you are aware of all of your rights, obligations, options, risks, and benefits.