Shane and Andrea got it on in the car after zombie hunting and nearly getting killed earlier his season. Dale's been pining after Andrea since season 1 but she's always rebuffed him. He was ready to die with her, remember?
Oh that's right I did completely forgot about Shane and Andrea in the car. But if she's rebuffed Dale at every turn then the've never had sex.
But as I said before, I think you're confusing drama with melodrama. I think that Walking Dead is a drama that is some times badly written and so slips into melodrama but that doesn't make it a soap opera. Case in point, Shane and Lori would never ever get back together (as they would in a soap opera/melodrama).