Dislikes Intensely:

Serenus Snape (due to their bad first date and Serenus bashing him over the head with a bottle in the brawl)

Family:
Sirius Black (brother)
Draco Malfoy (first cousin, once removed)
Lucius Malfoy (cousin by marriage)
Nymphadora Tonks (first cousin, once removed)

Regulus is unmarried and has no children...that he knows of. *smirk*

Friends:
Regulus has been walking the balance between good guy and bad guy since his appearance in the game, but now that he's officially gone over to the Dark Side, he doesn't have friends anymore. Lucius is the closest thing, but they don't trust each other at all.

Loathes With the Searing Heat of a Thousand Suns:
Sirius Black
Remus Lupin
Severus Snape (although it's more like a love/hate relationship since he's still carrying a torch for Severus as he has been for the past 20 years)

Lovers:
Hermione Granger (twice: here and here)
Severus Snape (although Severus doesn't remember their encounter before Regulus faked his death in 1980, due to being obliviated)
Bill Weasley (twice: here and here)
Charlie Weasley (twice: here and here)