jerrymichelle: "If one of your partners wanted to be in a relationship with another partner, how would you feel about this"

That's a good question for anyone considering "expanding" their relationship options -- would you want your partner to bring home another man/husband or woman/wife?

Polyamory can be an appealing option for people who are considering an affair but true polyamory requires that all partners have the capacity to take on other partners and that all parties of their own free will have consented to the arrangement(s). If the partner is unwilling and that sort of situation is forced upon them against their consent... it places that relationship in jeopardy, to say the least. Start adding in other factors such as children, in-laws, mortgages, finances, work, who's getting more time with who? The situation becomes overripe for plenty of drama and plenty of heartache.

Meantime, this link may also be appropriate to the original poster's question: How do affairs begin?