sexless relationship

I'm in deperate need of advice. As a classic "nice guy", every "real" relationship I've been in has been without sex. The women I date all have no problem hugging and kissing but I'm always pushed away when I want to go to the next level. There's this woman I've been dating the past few months who seems to be keeping me at the same distance. We have some really good times together and things get quite passionate between us, but once again....I'm pushed away when things start getting too hot. Unfortunately my only sexual experiences have been with casual acquaintences or even worse, one night stands...I'm just really missing the pleasure of sex with someone who acually means something to me. I'm afraid to bring this up with this woman because I assume for most people, the sex just happens....and I know this will never just happen with me so I need to take the steps to make it happen. I'm practically to the poing of getting on my knees and begging for it but I don't think that will help. Any suggestions would be appreaciated.