Unfortunatly the same scenerio is in the back of my mind. My hope however is that he'll feel the time and effort he's already put in are worth seeing through on. Its not just the progress of the first team, but the development of the reserves and youth set up. Rafa has been responsible for a lot of young signings that are now proving thier stuff at those lower levels, and could really pave the way for great things in the future. He may want to see that flower bloom.
To use your analogy of a cheating partner, its a question of do you cut your loses and get out, or try to work it out. Most marriages hit hard times, and sometimes you loose all trust so the best thing is to walk away, but sometimes you can see the foundations are solid, so its worth working and fighting to keep the relationship going.