This is Regulus:
Regulus is 17, pureblood, Death Eater. He'd probably really like Machiavelli if the bloke had been a wizard.Friends
Regulus generally gets along with pureblood supremacists, Death Eaters, and people who generally have the same socio-political beliefs he does. Regulus also tolerates people who are likely to be powerful allies (the wealthy, the politically powerful, the people he believes are going somewhere). His closest friends will likely be other Death Eaters or purebloods sharing his beliefs.
Are you a mudblood? You fall here. A blood traitor player? Here. One of his brother's friends? Yup, here. Someone who is actively working against the Dark Lord? You guessed it. Here. These people are all minor enemies, for the most part (though the latter tends to carry more weight on the 'enemy' scale). If you hurt his family, you vault up to the major enemy list. You don't want to be there.
Regulus is currently single, and he's not really looking, what with the war taking top billing for his time and attention. He wouldn't be opposed to a girlfriend, but she'd have to meet certain qualifications. For example, he isn't likely to get involved with a girl unless she's someone his parents would approve of. As he's a closet romantic, he'd probably be a rather decent boyfriend (when he isn't out causing mayhem for the Dark Lord), but any potential romantic interest is going to have to convince him that she's genuine and trustworthy, else he'll never let her in.
Ria is big on plotting, so plot away!