Why did he change overnight?

I was talking to this guy for a while, and we had gone to high school together, and he seems amazing.
I live about two hours away for school, and he's offered to come up to spend time with me, but because of my late classes and how much studying I have, I didn't want him to waste time to come up to barely get any time with me.
Anyway, we actually connected very well, and I felt able to open up to him about my issues with my family, and he opened up about some deep stuff too.
I have a break for school for over a month, and I was gonna spend it with him. We had all these plans, and they sounded so great. But as it got closer I got nervous. Although I had been broken up with my ex for over six months. It started to hurt when I thought about doing things with this new guy that my ex and I did.
I wanted to tell him in person how I felt, and I was nervous about it. The day he was going to pick me up, he swapped his schedule so he'd be off by 1 instead of 8 and as happy as I was, i knew he really liked me.
He brought me roses and he seemed so excited, but I couldn't bring myself to talk to him like I did while we messaged. And after a little bit, I felt really sick and I asked him to take me home. On the ride back, I told him about my ex and how I felt about things and asked if I could have some more time to be over him before we went any further.
He didn't really say anything, but he grabbed my hand, and I felt terrible. I asked if he was ok before I left, and he gave me a kiss on the cheek and said he understood.
But I went to message him this morning, and he seems to have completely blocked me.
Why was he so sweet if he was going to block me?
Why did he change overnight?
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