Straight Friend w/ Mixed Signals

So, I just want to get this out there and get a sense from others on how to deal with this situation. I have a friend, who likes to claim he's straight more often than my other straight male friends, who's been sending me confusing signals for nearly two years now. Here's the story. I can't go into specifics about how we met, but they were under extraordinary circumstances that brought us together one Summer in California. For this post's sake, let's call him "Casey." He's from the midwest, I'm from the east, but we hit it off almost immediately. We have the same athletic interests, music tastes, and I remember just talking to him about everything and anything for well above an hour while a few of our friends just sat and listened to us. Casey and I even belted songs from an Uber's pandora station. Anyway, that meeting was nearly two years ago. Since we both live in different states and go to college in different states, you'd think we'd drift. But no, we snap, text, skype, facetime, you name it. At first, he really grew to be one of my best friends. This is when things get a bit confusing, where the flags start going off in my head. When we text, he sends pretty endearing things. We've confided in each other on different occasions, and he's even told me how I'm the only person in his life he can truly be himself around, not the masculine facade he was forced to develop. Side note: we workout together when we video chat each other sometimes... Anyways, here are some things he's told me. He told me he wished I could be his plus one at a family member's wedding, he tells me how much he wants me to be happy, how he wants to be the one I lean on if things get rough/the shoulder to cry on, etc. This past Summer, he went away for a month where he couldn't use his phone. When he came back, he told me he thought about me everyday while he was out there. On my 21st Birthday, he wished me a happy birthday three different times. Once in a groupchat we're in, again as a text at Midnight exactly, then again on my Facebook. I'm supposed to visit him at his school for a weekend. This weekend is weeks away at this point, and he's already come up with a list of things he wants to do with me. Like, I've been around the block a few times with different guys, but no one's ever gone out of their way like this before. Whenever we talk, somehow the conversation leads him to telling me that he's straight. Okay, but why does he keep telling me this? I make no advances on him, I don't really say anything that involves sexuality, so why so often? Makes me think he "doth protest too much." Although our back and forth banter is a bit more intimate than most, it never crosses into anything inappropriate. I myself recently went away for a few months, I was doing a University Program in Europe, and I neglected to talk to everyone back home, so this included Casey himself. He told me from the very start he counted down the days, lurked on all my social media to check on me, and said how he talked me up to all his friends that Semester. He even listened to my favorite songs to "fill the void" I left in his life. One time, I had enough and asked him why he cared so much about me. He danced around it. He said things along the lines of, "You don't just leave your best friend hanging when he needs help." But I can read him well in that, that's an answer any person with a good moral compass would say. I wanna know why me specifically, after only meeting in person once nearly two years ago. I haven't confronted him about this since, but I plan on doing so when I visit him. He's my best friend, and I would definitely date him given the opportunity, but I'm not agonizing over it. I just need to know, you know?