Boyfriend is afraid of PDA?

Yeah, the question explains it all. My boyfriend is afraid of PDA, public displays of affection. And yesterday i wore a skirt to school and when i sat down at luch he yelled REALLY REALLY fast "YOULOOKPRETTY!" i didn't now what he said but my friend told me so i said aww thank you. and that's basically the only time he's complimented me. He hugged me once. ON FORCE. what shoud i do?