Everyone that knows arnold says he's the most generous guy and loves to give back, he doesn't forget anyone on his journey upwards. The persona back in the day was part of his drive to succeed but alot was also a persona to create controversy and attention to create his brand. For example we know he did actually go to his dads funeral.
From the books I've read Arnold always liked Lou but also knew he was never a threat in competition and knows he's very insecure. A comment from a few years back someone said to Arnold, lou says he's more muscular then you now. Arnold said well let him have that, he needs that more than I do right now.
Regarding Mentzer he never hated him but found it easy to wind him up, where as Mike took everything so seriously Arnold would always see the funny side of what he's doing but while giving 100%. Plus he always had this mindset of moving forward, not regretting and not looking back. Some people like Mentzer let things eat them up and destroy them.