skydiving tickets

Bought my boyfriend of 8 months skydiving tickets for his 27th birthday in a month and he reacted surprised but sort of dull.. 
usually when he's genuinely happy he shows it, but with this there was no genuine happiness. 
Then he just covered it up by saying he's a bit scared about the jump but i know there's something he's not telling me. 
Ugh. This sucks, now I feel weird and I don't want to bring it up to him. I guess if he wants to say something then he will. Thoughts?