He told me to stop by after I got out of the movie. We met in the parking lot outside his dorm and kissed hello, quickly, like something you do out of habit. I didn’t know then that it would be our last. He was tense, his eyes focused everywhere but on me.

I don’t remember exactly what he said, but he ended with: “I don’t think I can do this anymore.”

My heart pounded as he gave his reasons. I listened but didn’t process. I stood there in the cold, swaying nervously from foot to foot, my hands shoved inside my jacket pockets. I tried to respond but stumbled over my words. Normally outgoing and talkative, I couldn’t even form a sentence. Warmth radiated from my flushed cheeks.

As a student of neuroscience, I have learned that the most intimate relationship is the one between your head and heart. They talk like best friends via the common carotid artery, which sends blood from the heart to the brain at a running speed of three feet per second.

The brain has developed mechanisms to sense danger, and it responds immediately in the presence of any threat. When a threat is identified, an emergency call is made to the hypothalamus, the command center for our hormone system.