I am curious who In the couple typically starts these types of relationships.
wow, I think this is a tricky question, actually, because it really all depends on why the cuckolding is desired. Keeping the sex exciting between a couple that's been married 10-15 or more years CAN be a major challenge, and dangerous to the relationship if it is not addressed properly. That said, I think ......
For women, usually they cuckold their husbands because they're not being sexually satisfied at home ... he's become lazy, sex has become routine, he's terrible in bed, has a small cock that can't seem to please her, etc, etc. When a woman cuckolds her husband, its often about the affection she's missing at home, and hubby often doesn't even know she's screwing around on him. This is true cuckolding.
For men, its strictly for the excitement. Sex has become boring with the wife, and he needs help to restore his sexual excitement & enthusiasm, or because he's become
unable to sexually please his wife due to impotence, etc and is making concessions to allow her to find sexual gratification. It can also be because the husband has bi-sexual tendencies that need attention, and bringing another man into the lovebed gives him the chance to fulfill his homosexual side . I think a better word for a man who encourages his wife to have sex with other men is
wittol.
It's hard to say whether cuckolding is voluntary or actual cheating, as well over 70% of marriages have a spouse that cheats sometime during the marriage.