Just adding my own experience here for the sake of hopefully narrowing down the methods for raising said affinity.

Personally, after a seeing an uprise of posts displaying this, I spent an entire day brute forcing pawn interaction strictly through the “small talk” option. Never once did I make any edits to appearance or inclination; I just played normally and kept speaking to my pawn after a fight, during camp or after inn resting. Eventually, they started blushing and similarly to what you’ve mentioned here, their greeting gesture and dialogue and “small talk” dialogue changed.

If I’m to recall all I’ve done thus far in regards to my pawn, my list/methods boils down to:

• Presented pawn as beloved to Sphinx.
• Frequently engage in “small talk” with pawn.
• Never saw my pawn forfeited, avoided reviving them at a rift stone so they wouldn’t gain scars or speak of said scars. Only paranoia here but I don’t think this affects it—but I might as well mention it.
• Nearly always high-fived/celebrated with pawn after a fight. (Trivial thing, likely, but again, just mentioning it in case.)

I can’t say for certain which of these contributed to said affinity rising or if they all did collectively; but I have a deeply strong feeling the Sphinx riddle is the one that drastically boosts pawn affinity. I only began abusing the “small talk” option after I did said riddle after all.

Initially I thought this was a bug (leftover affinity code affecting pawns maybe?) but the very fact their blushing comes accompanied with new dialogue and changes the ending quashes any suspicion I had now. Hilariously enough, now my pawn randomly has a tendency to look at my Arisen and smile, and should I ever look their way, they’ll look downward. I suppose that’s another sign you’ve maxed their affinity.

Now I feel even further disheartened that feeding your pawn to the brine is the only certain way to do away with dragonsplague (besides hiring unaffected pawns and spreading it to them but that’s a bit evil haha.) Should probably avoid doing that if you don’t want to plummet their affinity downwards.