I'm so terrified of showing my feelings..?

I've been hurt badly in the past & I know this sounds cliche but I am so scared of showing my feelings. I'm with someone I really like at the moment & we have so much fun together, make each other laugh etc..but it never seems serious. I recently told him that I liked him a lot..he said the same to me, and seemed really hurt when I said I didn't think he'd feel the same. It felt good, but afterwards I felt so exposed and vulnerable. I feel like I'm setting myself up to be hurt again. I hate him knowing how I feel about him. He's quite easygoing, and doesn't take things seriously, so I thought for a while that he was just with me for sex. It's like I can connect with someone physically but not emotionally. And it's so frustrating when I think I'm actually in love with him, but I'm too scared of showing him how much I feel! Urgh! How can I get over this mental block?