I'm more concerned as to what he's doing to your finances during his mid-life crisis. He could be taking on debt - buying things for himself and for her - that you'll be responsible for paying HALF of, since the purchases were made during your marriage. Even if judge awards that debt for him to pay, creditors will still go after you for it if he refuses to pay.
You're in a pickle, since Texas does not have legal separation, from what others have written here.
While you WS is in a generous state of mind and feeling a little guilty (he will have no guilt later and will likely turn on you as his enemy), do what you can to get your names off of his charge cards and get your own. Or ask a lawyer what you can do to protect yourself financially.
Also, if he is in a home you own together, ask the lawyer if you moving out is considered abandonment, and automatically he gets it.
You do not have to file for divorce in order to get legal advice.