I know the age of consent in CO is 17, known that for quite awhile.

My point is that teenagers (boys AND girls) are walking hormones and have "desires" just like adults. I had one or two hot teachers in school, if one of them showed that kind of interest in me I know I would have jumped at the chance to "score" with one of them. Unless the coach was blackmailing her into creating a "relationship", the girl had to have some interest in the coach for that to continue for over 10 months.