I have this problem rather often, personally. I get attached rather easily when I get a good first impression of someone, and I find myself wanting to spend all day and night with them. Although I really only want to be friends with them, I often mistake it for an emotional boundary that cannot be crossed, even though I don't know what it is exactly that I want to cross. Usually, if I give it enough time, the confusion/feelings fade and I realize one of two things: One, I really do like them, and so feel like I must tell them what I feel, or Two, I just want to be friends with them and I enjoy their company a little too much, and deem it selfish to continue doing so, and thus limit the time I spent with that person.
Not saying that's how it will be with you, but it's just how I deal with it.