wrote:

These findings fall in line with what is already known about the characteristics of the various attachment styles. Securely attached adults tend to have a positive sense of self as worthy of love and they trust others to reliably supply that love. They have the emotional reserve to weather the inevitable difficulties that will arise in marriage.

Well, let's not delude ourselves into thinking that being securely attached guarantees that your partner will have a strong libido and want to continue having sex with you. It doesn't.

I think what happens is that when security attached people go outside their marriages, it's more often because their partner has been unwilling to have sex with them for a long time and has been unwilling to try to solve the problem. They tend to have fewer outside partners because they securely attach to just one outside partner as a close "friends with benefits", etc., whether as an open marriage or by "cheating".