I think Roy Harper gets a "free pass" on promiscuity because that's been part of his character for forty years. In fact, it's what made him a distinct character.
Back in the early 1970s DC realized that the only thing it could do with Roy is make him the anti-Dick Grayson. Robin represented upright youth; Speedy did heroin. Robin had a steady girlfriend; Speedy flirted with every female. Dick played guitar; Roy played drums. (Okay, I'm not sure about the significance of that last one.)
Then in the 1980s that went further, and it turned out Roy had had a sexual affair with a villain. And didn't use a condom. (Dick, in contrast, was in a long-term monogamous relationship with a fellow hero, with no surprise pregnancies.) Furthermore, Roy didn't tell his teammates that crucial fact about his past until the middle of a mission. We saw those revelations play out in an Action weekly series that featured Nightwing and Speedy together as a way to heighten the contrast between them.
Roy gained custody of Lian, and the contrast has continued in a curious way. Roy continues to sleep around casually, especially with female heroes; see Outsiders, passim. He's a "bad boy." But he's also a family man, devoted to his little girl. Dick is usually portrayed as a "good boy," seeking committed loving relationships, which makes some of the stories about him (e.g., Nightwing Annual, #2; Bruce Jones's run) so out of character. Yet Dick is also the only member of the early Titans who's never settled down with a spouse and kids.
So we've come to expect Speedy to screw around, and screw up, and he does. We've come to expect Nightwing to be nearly perfect, so we hold him to a higher standard.