It didn't take a genius to see that Patty was uncomfortable with this whole thing. Part of Barry thought that maybe he should just leave now rather than attempting to explain himself. He knew his explanations weren't going to change anything, but he still cared about her. A lot. And since there was no danger here, he felt like he could actually be honest.
He sat down next to her and leaned forward on his legs. "I'm sorry," he said. "I know that doesn't mean a lot, but I wish I could make you understand how sorry I am. The last thing I wanted was for you to leave Central City, but... it wasn't about what I wanted. I had to do the right thing for you and that was letting you go."