Theirs is first relationship established in the Chronicles through Interview with the Vampire. Lestat made Louis because he was lonely and because he thought Louis very beautiful. Louis was wishing for death but instead Lestat gave him life. Theirs is sort of opposites attract – Lestat is a fun-loving , risk-taker and Louis is a nagging, depressing baby (though I love him). The fact that he has been mourning his whole vampire life makes us wonder why Lestat puts up with him let alone loves him. But Lestat is so loving of his fledglings and his friends that perhaps it wouldn’t matter what Louis was like because the love was there, at first sight perhaps, whether or not Louis was made out of recklessness.

"I...truly wished to be murdered. And then I was attacked. It might have been anyone... But it was a vampire."

Louis seems to be quite hesitant however, throughout their whole relationship, to be committed to Lestat. It seems to be constantly searching for someone else to complete him. You’d think that after losing both Claudia and Merrick, he would turn to his maker. He needn’t look so far for love. But every once and a while, usually when Lestat’s not being a brat, we see Louis’ affection of Lestat. During and after the events with Akasha in QOTD, we see that Louis is appreciative of Lestat and acknowledges what he came close to losing. However, it gets rocky again during Tale of the Body Thief when Louis gets angry with Lestat’s recklessness (yet again) when he switches bodies with a mortal but as soon as Lestat is incapacitated at the end of Memnoch the Devil Louis is there for him the same goes for Gabrielle.

“Do you love me now?" I asked. Oh it was excruciating to watch his face soften and brighten simultaneously as he smiled. “Yes.”

There is also a good reason for Lestat to be there living with Louis, Merrick and David because if Lestat wasn’t there with him Louis and David slight competition with Merrick might get out of hand. Lestat and Louis’ relationship sooths the other relationships around, especially with Lestat’s other fledglings.
When Louis seems to believe that Lestat’s love perhaps is not active or that Lestat isn’t really demonstrative in his actions. But when Louis tries to kill himself, Lestat awakes from a coma to save him. They are snuggled together on the couch at the end of Merrick, which is so cute. Then Louis finally allows Lestat to give him the blood to make him as strong as David, which is so cute. Then Louis finally allows Lestat to give him the blood to make him as strong as David, which he had until then refused.

"You are a perfect devil, Lestat! ... That's what you are! You are the devil himself!"
"Yes, I know... And I love to hear you say it, Louis. I need to hear you say it. I don't think anyone will ever say it quite like you do. Come on, say it again. I'm a perfect devil. Tell me how bad I am. It makes me feel so good!"