Sean was a very proud individual. He was still young, after all—something he was constantly reminding his peers of as a way to tease them. He was the best of the best, an aspiring gunslinger who'd be well-known throughout America. He'd go out with a bang and leave a lasting impression on American history. Now that seemed perfect.
Sean could also be susceptible to jealousy. Particularly when it came to you—or alternatively, those who flirted with you. Sean, of course, knew you weren't his, and therefore had no say in who you spoke to or what you got up to with said people.
But...still. Could you blame him? You were practically an angel—to him anyway. He knew others would have very different words to describe your looks. And when you inquired as to whether he was jealous, well...
"Jealous? Me? Pfft - never. I don't get jealous, thank you. What's there even t'be jealous of? His terrible hairline, or the way he breaths with his mouth open?"
Was he in denial? Of course Sean was; a blind person could see that.