@AnonMomof2 , your experience wasn’t unusual either. These folks are just doing their jobs, so if you got from your encounters what you needed, great - you didn’t add to their workload! Some applicants engage to show interest and be more memorable. It can work. Or not!
If you write, short and sweet is fine. It can be factual, as ski’s above is, or it can be more of "it was a really hard decision, made more so because we felt a connection with you, but I’ve decided to attend xyz. Thank you for everything. "
They expect to do this with many students every year. For you, it’s different!
I’d have no problem with informing the coach first so long as they weren’t going to try to change my mind.