Why do I feel like I'm going to explode when thinking about him?

Me and this boy has been friends since 7th grade and I've had a crush on him in 7th, we are now in 8th. I hadn't talked to him in a while and I found him again in 8th grade, we started talking again but through text now. I still have a crush on him and he likes me back. But him telling me that, I feel really happy and my chest is tingly and I want to explode..
Why do I feel like I'm going to explode when thinking about him?
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