I've been in it for 20+ years. I've known coupes who have been in it 30-40 years. I must say it varies by age. I've met couples in their 70's (yes one of the hot wives I fuck is in her 70s .... fucking gorgeous with blonde hair, and fake tits, yummy, and they didn't get into it until 3 years ago). Her first Bull happen to be a black guy. He was married and when Bulls are married that just causes complications.
I've also people years ago who did the kinkiest stuff you could imagine and now 20 years later are 100% vanilla (thought not boring they just dont' play anymore). There is really is no set mold. Some couples come into it late, some early, some stay, some leave, some the husband is the instigator, some the wife.
I have seen some marriages fall apart. But (and I'm not privy to all the details) it never seemed like because of the cuckolding. But more the Bull pursing and ultimately "winning" the wife. The Bull at some point, usually very early on, decided he wanted the wife for himself. And that is the biggest danger I see if you want the marriage to stay together. The wives want to be with Bulls sexually, many times romantically (80% of wives I've fucked have used the L word). All this can add to the intensity of tje relationship, but the Bull needs to be a gentleman and not try and take the wife.
As one of the first guys I cucked said to me "You are already fucking my wife, you don't need to take my marriage too."