Not really because Regulus was his parents "good boy" whenever he did something wrong his parents would probably say "why can't you be more like Regulus?". Also he joined the Death Eaters (he did back out, but Sirius didn't know the extent of it) so Sirius probably hated him as much as his parents. He probably was angry though when he heard Voldemort killed him.

Considering Sirius doesn't shy away from telling Harry what he thinks about his family, it seems notable that he only calls Regulus "my idiot brother, soft enough to believe them" (and again, a "stupid idiot"). Sirius seems to regard Regulus as less an irredeemable bigot and a murderer than a kid who got in too deep and got killed trying to back out. Which makes it sound like he did love Regulus, or at least recognized that Regulus was as much a victim of their abusive and toxic family as he was. And he tried to investigate Regulus's death, which isn't what a busy Order of the Phoenix member would do if he didn't care.

Regulus obviously never speaks about Sirius himself (and no one else comments on their relationship), so we have no idea what he thought about Sirius. I like to think he cared as well, but the evidence just isn't there either way.

^Also, Regulus was obsessed with Voldemort, and Sirius hated Voldemort. Big difference right there.

No.

1. Sirius hated his family.

2. Like Moon765 said, Regulus was the "good child" and Sirius would probably be compared to him all the time.

3. Regulus was a Death Eater and he always talked about Death Eaters.

4. They were made as rivals, coming from rival Houses.

5. They had ENTIRELY different beliefs, friends, lives.