Please don't let this make you sad. I'm telling you because I promised never to keep anything from you even if I don't know what it was myself, and I want to work it through with you. And if you turn this into "you shouldn't be with me" I'll be angry, so don't.
Ever since I got your email that one morning saying "that's an interesting way to look at things" I've just gotten a sinking feeling in my stomach whenever I talk to you. I love you more than anything. You're wonderful and perfect to me.. so that's probably part of why I'm upset. But I don't get what could be making me upset... I know you've noticed. I had trouble even responding to your email this morning.
I hope this doesn't ruin your day. If this interferes with your work I'll be mad at myself.
I love you, and I always will. I mean that.