Highest i have seen so far is 60 Buff for Pamu. Not unlocked lover level for anything beyond her, my latest was Alpha. Alpha required you to be a love doctor which is 50 in two hobbies. Eva was surprisingly easy so far. Well "easy" she needs silly amounts of affection to reach every tier but she hasn't needed any hobby/job levels so far. Just a date or a gift for each tier. I don't max her though because it takes eons to get anywhere with her.

For the 60 buff - as i said before, even at my current prestige visible in the picture above it takes 10ish hours to reach from level 50 to 51 in a hobby.