I think this is triggering something for you. It sounds perfectly normal. How would any of us make new friends if we couldn't keep increasing the intimacy of our connection? You already took a day trip to Philly, so it's not like you're just "had coffee twice" friends.
I've struggled with friendships as an adult. When you're young, you have so much proximity in the same place in life. As you get older, that changes, so you have to be more proactive. I've spent a lot of time wishing I was closer to certain women, yet lacking the confidence to purse them. On the flip side, I've had women pursue a close relationship with me that made me feel like, "Wait, what? We're not that kind of friends?" So maybe that is my fear of being known, or of being rejected, talking.
In any event, I'm going through a divorce, and that has made me go deeper with a lot of my friendships, and I'm very happy about that. But I wish I hadn't waited for a crisis to make it happen.