Do you guys have funding? If so, you will have to be respectful of the trust that your investors placed into you three as people. It's your duty to your investors do what's best for business.

Totally understand that passion is hard to control. In this case, especially if outside capital is involved, I'd say "mind over body."

If there is no outside capital involved you'd have to consider the trade-off startup vs. love. That's your private decision and don't let anybody judge you no matter what you end up deciding. Make sure that you have a convo with her before you make a decision. You wouldn't want an expectation mismatch after you have given up your startup for her. If you decide for the startup and against her you should also have a serious convo about not having hard feelings when working together in the future. Good luck!