The emotions ran through him in rather different ways. Having not planned what he was going to say, even in his head, so that he would not self-edit, either not to say what he meant or to be sincere in that way politicians are sincere with the public, Sirius didn't quite know what all he was going to say, where exactly it might spin off to. However, he knew he was going to say it. He wasn't holding back. And he needed to say it, say it to Oscar, so that there would be closure. With that, he would move on. He'd move on because he had decided that was what was best, for him, for his family, even for Oscar and his family.
''The entire time I've pursued you, it hasn't just been a crush or infatuation or flirtation for the sake of it, for fun," Sirius began, "I started liking you long before that. I want to find the love of my life, I want to fall in love with him, and I want to spend the rest of my life loving him. I want him to know my family and my family to know him. I want him to be a part of my family, and mine of his. I'm not going to give up on that, whether I'm here or back home or exploring the final frontier.
"Flirtation and casual encounters can be good," Sirius continued, "I'm fine about what happened with Sirius when I was younger. But that's not what I want, and with the small town feel of this place, it's not something I want to continue engaging in here. I pursued you because I believed we had a chance. You weren't meant to be some unattainable target because, well, I don't believe in those but I also don't see that as doing me any good. You weren't someone I could fall for so as to avoid dealing with real entanglements and real life. It's real. It's serious." He was aware of the bad pun, but the word had just fit right.
"Despite what you've said about me not knowing you, not really knowing you, I've spent a lot of time doing just that, between talking with you and with your wife. I know there's more about you I don't know. That's true about everyone. Falling in love isn't about knowing someone completely. That's what staying in love and having a relationship is about," Sirius truly hadn't known it would take this path, but it had, "I'm in love with you."
Though he had a small pause because that wasn't just something to say casually to someone, and it wasn't casually done. That realization had come on much earlier, though he hadn't told anyone because Oscar deserved to hear it in person and because he deserved to know before any of his fellow scientists did. "I love you," he continued, "I doubt that will ever fully go away. I don't stop loving people."
"I'm not trying to change your mind," Sirius made sure Oscar understood, "I respect your decision. I respect your reasons. I am the last one to want you to lose your position. And I don't want to be the reason you could no longer try to save your world and help your family. I feel the same way about mine. They're more important than you are. That's why we cannot be together after this experiment is over, either with me staying with you or you coming to my world. Our families and their lives are more important. And we cannot be together here, for the reasons you gave. That means we cannot ever be together.
"I'm not going to wait on some whisp of a hope some boss of yours is so moved you're allowed both, your job here and me. That's not how people operate where I come from, and I suspect your bosses have their choice of entertainment if they want to watch a romance. So I have to get over you. I'm going to fall out of love with you because that's the only way I can be healthy. Ir's what's best for me.
"You'll always have a place in my heart, along with everyone else I love," Sirius concluded, "But we're through, romantically."