My boyfriend wont really express himself in public. Wat do u think is going on?

Its my birthday. Im turning 20. My bf is already 20. We've been together 6 months 2 weeks 4 days. We've nvr argued, we love each other more than anything, trust each other unwaveringly, and are extremely affectionate towards each other. Butg h notice in public, not really general public, but his friends and stuff he dosnt seem to want to kiss me and his 'i love u' s are muffled and low. It kinda of bothers me cuz im so affectionate to him everywhere and his is to me to. Except in front of his friends. Ive tlkd to him about it and how it makes me feel. Like he dosnt want to be on me in public. I told him if he wants i can leave him alone in public. He said no, and if i want he'd shout how much he loves me. So i said yea. He said it louder he didnt really shout it. Jus said in a normal voice. And at the time his friend wasnt even in da room, so it really dosnt count. I dont understand it and it saddens me he'll be so lovey dovey but not in front of his friends. Ive confronted him about it more than once.