I know what you mean. Join the club hun, you are not alone. My ex, whom I dated for 2 years did it too. Try to break the silence with music, if in the car. Try to keep each other occupied, instead of thinking about what you aren't talking about. On the other hand, don't rule out secrets. Get him to talk when you are intimate. Not talk, no intimacy. Ask questions, and dont' be naieve. Overall though, it is probably nothing, just a guy phase. You might also try not talking to him. He will get sick of the silence too and eventually bring things up.

Sometimes,it means nothing,except that he is comfortable enough with you to not need to always be talking.If the silence is a regular thing and you two never talk,that's different,but if he does not feel the need to chatter all the time,enjoy the mutual silence.
Patty

Well i'm a guy... And i've done this to my fiancee also, my reason was having alot on my mind, and not keeping myself occupied ( for instance being sat in a car ) your mind wonders and begin to think... My mum was one for claming up and not talking about her problems and, out of all the things I could of inherited from her, I got the claming up too! ( grrr damn you mother :d hehe ) so this may be his problem, he may be depressed about something, or he could just be tired...

If this is the problem you may find it hard to get him to talk about it.

Ah ha! My hunny does this all of the time....I've gotten to the extent where I don't converse back, then I complain...And all this does is irratate him,,and not in a productive good way.
My only suggestion is to distract yourself! Turn on some great music and sing it like you are alone in the car...Make him laugh and enjoy eachothers energy, even if not in conversation

Qtpatuty30,
I always do the same thing as u, like me and my man will be walking around or driving somewhere and he will sit there in silence and I always start to conversation, then when he doesnt respond back to me as he usually would with like one of his friends, I ask him whats wrong and then when I ask that he always yells at me, and says:( nothings wrong with me, your so annoying, im fine, leave me alone.....Etc.) I know exactly what your talking bout. Im afraid too, that hes hiding something from me and that he might want the relationship to end soon.

My b/f is the same way in the car at home.