I don't think divorce can be avoided in a sex-oriented society. Modern culture emphasizes sex over a "household alliance", and it's then not surprising with divorce. Monkeys also tend to switch partners every now and then, so perhaps we're hard-wired to act that way unless we're given an upbringing that makes us change opinion. The problem with divorce is however the children, who often get alienated, become bullied or bullies, and may get problems with their education. If we wish to have sex and relations like cavemen, we probably need to have herds collectively raising children like cavemen, so the partner switches of parents don't drastically change the living situation of the children (this however requires switching only between the partners within some designated small enough herd, which may not be enough for some). I don't see any solution to the problems except either sticking to traditional culture family values completely, or reintroducing herds completely. The compromise between the two doesn't work very well IMO.