I hate Amy and Sheldon's relationship. He is asexual. Period.
Apart from that, I fucking love it.
"Some asexual people engage in sexual activity despite lacking a desire for sex or sexual attraction, due to a variety of reasons, such as a desire to please romantic partners or a desire to have children."
Also http://www.salon.com.../05/26/asexual/ which features multiple people who are asexual discussing events in their lives, including multiple occasions of making out, masturbation, etc.
Asexual doesn't mean you can't be in a relationship. Additionally, being asexual doesn't mean you can't be romantically attracted to someone.