Of course they had sex. They are vampires and obviously attracted to each other. And there was the bonus of mocking Spike by doing it. The way i see it the great love with Drusilla was pretty much all in Spike's head. And why would he turn against Angel if all he and Dru did was flirt?
Drusilla might be crazy but she isn't stupid, nor is she some damsel in distress that Angel can manipulate. If he had pulled that trick on her, she might have turned against him, not to mention it depends on the assumption that sex is a big deal amongst soulless vampires. I don't think it is. They slept together whenever they felt like it, they had their quarrels at other times, no hard feelings. Spike is the exception, the guy who has some weird notions about fidelity wildly out of place in the vampire world. Drusilla enjoyed playing Spike against Angel and vice versa. She has most likely been doing that for years before Angel got his soul with the added bonus of sometimes pissing off Darla too.
To play with Dru. Come on! He could have killed Buffy numerous times but drew pictures of her and what not. Imagine Dru being all hot and bothered thinking 'this time he will for sure' and not. It would be more like Angelus to flirt and be ready and then not, than it would for him to actually follow through. Angelus lived to screw with people, but not necessarily screw with people. Getting Dru thinking he would, and Spike thinking he does/did simultaneously for a person that likes to control others would be golden! and then he could sit back and laugh at both of them for thinking its happening when it never is.
Drusilla might be crazy but she isn't stupid, nor is she some damsel in distress that Angel can manipulate. If he had pulled that trick on her, she might have turned against him, not to mention it depends on the assumption that sex is a big deal amongst soulless vampires. I don't think it is. They slept together whenever they felt like it, they had their quarrels at other times, no hard feelings. Spike is the exception, the guy who has some weird notions about fidelity wildly out of place in the vampire world. Drusilla enjoyed playing Spike against Angel and vice versa. She has most likely been doing that for years before Angel got his soul with the added bonus of sometimes pissing off Darla too.