On the one hand, Lucas was grateful that his dad was just telling him the truth. On the other hand, he really wanted some kind of reassurance that everything was going to be okay. He didn't want to lose Riley forever just because he was dumb. His older self was definitely dumb too for leaving him all the info and money and stuff, but whatever. Ultimately, he'd been the one to ask and he'd screwed it all up.
"I just- I thought it would be reassuring! I love Riley and I want to marry her and I don't care how long it takes for her to want to do more than just kissing or when we get married or anything like that. I just care that she knows how much I love her and want to be with her for the rest of my life. No one's ever going to be as awesome and perfect as Riley is." Lucas did know that Riley wasn't perfect, that she held herself back out of fear a lot of the time, but he didn't want her to think he would ever stop loving her. Even now, he loved her so much it hurt.