My STBX just walked out and abandoned me for “other interests.” I owned my house before we were married, and my name is on the deed alone. I have a stepson from another marriage that I would like to leave my house to.

STBX is dragging his feet on the separation agreement because he wants everything we bought during our marriage. Can I write up my will so that my stepson can inherit my property?

While the home is your separate property and bought prior to marriage, if it was used as your marital residence then it would still be a part of the marital estate. This is relevant to equitable distribution. If you want to leave the property to a third party in your will, I would consult an estate attorney on that issue. It is probably better for you to resolve the equitable distribution claim (if there is one) first. If your ex doesn’t file for ED before the divorce is final, then he is estopped from ever filing it.