If you suddenly yawn during a conversation with ur one and only crush, then make sure u say something like, "oh wow...i'm tired...what time did you go to bed last night?"( but if u yawn while he's talking, don't cut in to make this vital comment!!! he might think you are too bored with what he's trying to say!! say this comment after he finishes whatever he's saying!!!!)
saying that one line will ensure that he doesn't mistake ur yawn for a yawn of boredom and it will open up a new conversation about bedtimes and so on!