Guy's Behavior

Why would my boyfriend act so shy and timid around me?

i am 25 years old and he is 24, we have been dating for about 7 months. I just don't understand his actions though. he acts very shy when he is around me and quiet. when he walks in my door he doesn't come up to me and give me a huge hug and kiss, he just comes in and says hi very quietly and puts his head down and sits on my couch, or comes up behind me and puts his hand on my back then quickly removes it. when we are out he never smiles he looks like he is nervous as hell. I'll say something silly and try to get him to be silly with me but all he does is go "hmm" and make a fake, nervous laugh. he always looks SO serious unless I make a super crude silly remark or get him drunk then he kinda loosens up. he does everything for me, he buys me things when I tell him he doesn't have to, he always tries to impress me by taking me nice places, he constantly tells me how beautiful I am sometimes way too much. but if he though all of this wouldn't he show it more when we are together? he never tries to hold my hand, never hugs me or tries to kiss me...the other day my back hurt REALLY bad because we were in line for a club and it was really long, so I backed up against him and said "can you please rub my lower back?" and he just lightly touched the area like he was scared and tapped it a few times. I felt really bad like I'm ugly and he doesn't wanna touch me...then inside I was dancing and said "dance with me!" and he wouldn't. I'm not ugly, yet not beautiful in my eyes...but I AM pretty so I don't understand why he'd be like this. I've seen pix of his exes and they weren't even good looking but he looked so happy with them. what should I do? what could be causing this? thanks. =)
Why would my boyfriend act so shy and timid around me?
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