Guys, Why am I so dense sometimes?

Am I the only girl here who chooses not to believe that a guy likes her. I was going over my chat log with this guy I'm talking to on Facebook and as I look back on it, this guy has liked me this whole time. I will provide the screenshots but I don't want him to see it. He wrote down, "I like u." My response was, "That's cool." Then he said, "great." When a guy says they like you, they mean they ACTUALLY like like you? And not just like you as a friend? When he said that, I assumed that he likes me as a person because I was nice to him. This was back in 2016, and I just got out of a relationship at the time. My ex and I broke up in 2015, and he wrote that 6 months after my break up. I admit that I was slow to pick up on it, and I'm just now seeing it. Someone told me I was naive.
Guys, Why am I so dense sometimes?
Post Opinion