This concept of pre-engagement really weirds me out. The "I know he's picked out a ring and is going to propose" stuff. If you know about it, and he knows you know about it, and you're both in agreement about the whole marriage idea, how are you not engaged?
Two adults who have decided they will marry one another fits the definition of engaged. If he knows you're marrying him, and you know he's marrying you - that's engaged.