What is Juliet apologizing for In truth fair Montague I am too fond?

Answer 1

She is apologising for not playing by the rules of love. The rules of love went like this: The man protests his love; the woman rejects him. The man continues to protest his love, now saying that her refusals are killing him; the woman continues to reject him. The man continues protesting, the woman keeps refusing, until finally he wears her down and she relents. In his relationship with Rosaline, Rosaline played by the rules. She was one of those "too cunning to be strange". "Strange" here means "aloof", the way the woman is supposed to act. But Juliet has let the cat out of the bag when she thought nobody was listening. She says that she "should have been more strange", but it is now too late--she cannot now pretend that she does not love Romeo.