If someone has the option to fix their marriage and save it or make bread for Shabbat (which would put fixing the relationship on hold) which one should be the priority?
I'm afraid your question assumes a great deal of information we don't have here, and would really best be addressed to a competent rabbi in-person.
But for theory's sake: assuming one could easily buy bread -- if baking it from scratch themselves would cause a strain on their marriage, then they shouldn't do that and should instead buy.
Baking bread from scratch is a nice-to-have that could maybe be a fulfillment of "doing extra to honor Shabbat." There's been a recent resurgence in treating baking as a big ritual thing. But keeping peace in the home is even more important, and was in fact the main reason the Sages instituted lighting candles on Friday night.
Now: if someone has only one candle on the Friday afternoon of Hanukkah, the Talmud (Shab 23b) says better to light it inside as a Shabbat candle, than light it outside as a Hanukkah candle, as having it inside will promote family harmony, which is more important than declaring the miracle to the world (outside). And same thing with the wine for the qiddush:
נר ביתו וקדוש היום, נר ביתו עדיף, משום שלןם ביתו
"[If one has to choice between Friday's night] candle and [to make] the qiddush, candle is better, because of house harmony."
From this source, the preference is even over no wine at all to say qiddush on it.