Arrow's most heroic qualities also make him a terrible lover
Arrow may be one of DC Comics' greatest heroes, but what makes him a hero is exactly what makes him one of DC's worst romantic partners.

As one of the few unpowered superheroes to make it to the Justice League, Arrow is undoubtedly one of the best heroes in the DC universe, but the same instincts that earned him a place in the League also make him a fearsome lover.
Arrow had many love interests in the comics during this time, but none more famously than Black Canary. Oliver Queen and Dinah Drake's relationship is almost as iconic as Clark Kent and Lois Lane's. In addition, Oliver himself has saved the universe many times, and recently helped the Justice League rally against the forces of the untouchables during the dark crisis on Infinite Earths. Not to mention that Arrow also has the most important duty in the Justice League to protect the identities of other members. But despite this, his instincts that make him a great crime fighter don't always lead him to noble actions.
Dinah was Oliver's only true love, but that didn't stop him from having an affair with Black Lightning's niece, Joanna Pierce. Readers finally got Green's explanation for this Arrow #35 by Judd Winick and Phil Hester. After finally having enough of his young sidekick Mia Dearden snubbing him, Oliver bursts out with a confession about how he betrayed Dinah. He goes on to explain that he doesn't know why he's doing it, and he can only assume it's an impulsive instinct that makes him fight villains. The instinct that made Oliver a hero also doomed his relationship with Black Canary.
Oliver Queen Doesn't Think About Consequences

Arrow's willingness to fight heavyweights like Darkseid and Doomsday with nothing but a bow is also the exact reason why he is a bad lover. Oliver doesn't think about the consequences of his actions, which is a nice trait to have when running into a burning building or chasing a crazed gun-wielding criminal. However, when he is already in a relationship, this ability to not think about the consequences is not an advantage when an attractive woman asks him for sex.
Arrow is not the only hero with heroic traits but also a major flaw. Batman had this problem in Kevin Smith and Walter Flanagan's movie Batman: The Expanding Cyclone #6. Considering Batman doesn't even trust the team he's assembled, it's no secret that Batman is a paranoid. But that paranoia was on full display in this issue when Batman attacked his fiancé. He rips off part of her hair for a DNA test, just to make sure she's not some perfect robot created just for him.
Arrow is an amazing hero, but the exact traits that make him and characters like Batman so heroic and self-sacrificing are the same traits that make them the worst romantic couples in the entire DC universe.