Should I come out to my Coach?

I have a coach at my school who I've really bonded with. Starting yesterday I began to consider informing him that I'm non-binary. I don't know exactly why I have the desire to tell him, I'm not very bothered by the fact that he calls me Ma,am every so often, I don't get offended that she calls me she. I guess I just want to share as much as I can with him because as a kid with Selective Mutism I don't speak to others as easily as I do with him. I'm basically wondering if I should tell him how I feel about my gender or if it's just useless information to him. I'm worried who won't care, or think it's a phase, or that he'll be like my principal who's a major homophobe and transphobe. If you guys could give your opinion I'd really appreciate it.