I'm a guy, and I'll be brutally honest with the way I view kissing:
I personally don't really like kissing. But I know most women do. I view it as a stepping stone to my ultimate goal: sex. To me, a passionate kiss is a signal that she's really sexually attracted to me and would like to have sex. However, a couple of women I've dated had no intention of having sex - they just wanted to passionately kiss. Let me tell you, from a guy's point of view, that confuses the hell out of us! It sends mixed signals.
Some women just like to passionately kiss, and enjoy it, and just leave it at that, no sex or anything. From a guy's standpoint, passionate kissing can get our juices flowing if you know what I mean, and our arousal progressively increases. Our bodies are kind of programmed to have an ultimate release, which is orgasm, preferrably through sex. To get us all sexually charged through passionate kissing, then leave us without sex, leaves us, well, sexually frustrated.
Don't get me wrong, passionate kissing can be fun and enjoyable. But kissing just for the sake of kissing, as an act unto itself and not as a stepping stone to eventual sex is like a waste of time to me.
I'm sure many guys don't agree with me, but this is the way I view things, and your boyfriend may also.