crime fighting girlfriends
I don't think it's because of the playboy status. I think it's because of how the character is portrayed. Because of his commitment to crime fighting but the not girlfriend, the relationships wouldn't work out. But out of ALL the women he has dated & loved, Cat is the only one that has stayed around in his orbit and the only one he has grown closer to, grown in his trust and in his love for her over the years. But because they are on opposite sides, so to speak, DC likes to tease them more.