Wow, I am in a kind of a similar situation (just posted about it) so I know how you feel.
Speak from your heart, it’s always honest! I agree with Luke, and I’ll add put in a smile face or let him/her know that if the email is coming off as intense or dramatic, it isn’t meant to and that you just need to speak your mind.
Start by doing a few drafts, it doesn’t have to be perfectly worded, as long as you make your point and explain how you feel and why in a respectful way.