Recommendation letter by significant other if you worked with them professionally? My significant other (SO) and I are in five years of relationship. We met working in a lab and she already earned her PhD at that time. I was a graduate student. She was the main person I went after my adviser if I had logical questions about my project and helped me the process throughout. We now have two publications together. We worked professionally together for almost three years. She knows my potential both personally and professionally.

I am wondering if it is okay to use a letter of recommendation from her to apply for a PhD program. 
Updated: I edited the word "supervisor" as suggested by a commenter. She wasn't an official supervisor but, provided tremendous help with analytical issues. We also stay collaborating on other research projects until today even after we both were out of the lab.
No. If she discloses your relationship in the letter, the reviewer will likely disregard the letter completely, and may question your judgment for having asked her for a letter. If she does not disclose your relationship in the letter, that is a serious enough omission that it could have consequences for you later on (I can't quite tell where you are in your career, but the more senior you are, the more severe these consequences could be).