Alma knows that Brian is queer, although everyone assumes that she doesn't. A sheltered Jewish upbringing is one thing, but she's been in show business since before Brian had his bar mitzvah. A girl gets to sense these things. Being engaged to Lionel Bart probably helped. If she were directing Brian on stage, she'd tell him that his protestations of devotion need more conviction. He's never mastered the "I love you bit" (as the song she sang with Lionel goes). He's never even tried. Quietly she respects his honesty. Quietly she leaves the room whenever he steels himself to propose.