Can spouse claim adultery that happened after she left a letter of intent to leave our marriage on the door of our house?

Any sexual intercourse with another person during the marriage before a divorce is final is technically adultery.  She can make the claim and you can try to defend it by saying that it was after you were already separated and was not the cause of the breakdown of the marriage.  It will ordinarily not get her anything anyway, unless she can show that you spent marital funds on your paramour.  She should not be able to obtain spousal support from you, if you were not supporting her during the marriage and if she cannot show that she needs it.  It's possible that her lawyer simply through that claim in there without really expecting to follow through on it.  Some lawyers are sloppy this way.  This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.