Does precum come out right before semen? ive seen things that say it can come out anytime a man is erect, but my fianc says thats not true and that it only comes out right before ejaculation?

Precum is a layman's term some use to describe the mucus that sperm travels in. I call it semen. It is a carrier fluid that is protein based. It fills & lines the inner tube of the erect penis and carries the fragile sperm as a protective environment. During a male climax there is more sperm per amount of this fluid. All of this fluid may have small amounts of sperm. Your fiancé is misinformed.

Precum means different things to different people and despite becoming part of common usage, in my opinion is confusing. On sexual excitement glands in the passageway secrete a smooth fluid the intent of which is lubrication. It is not ANY part of ejaculation. It will stir occur if for some reason ejaculation does not happen.