This is something that you have seen in a lot of older, naughty movies. You may have had a threesome, but you are more interested in learning about cuckqueaning. You probably have a lot of questions, and that is okay. It is better to do research and then test it out to see if it is something that you can enjoy.
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What exactly is cuckqueening?
What is cuckqueaning? Well you probably heard of cuckolding. That is where the man gets off watching his partner sleep with someone else. This can cause them to get extremely turned on while watching his partner sleep with someone else. So, a cuckquean is a woman who gets really turned on by watching her partner sleep with someone else.
However, jealousy can be a nasty thing in these types of relationships, but there are instances that cause people to become very turned on by feeling the jealousy and then they make it work.
So, the other person is often referred to as a cuckcake, almost like cupcake, but not quite. Although, based on your comfort level, you may be the one finding your partner someone else to sleep with or they may find their own. You may just have a fantasy and not actually want to meet the person that your partner is sleeping with, which may be a form of jealousy.

Some practical points
It may also be best that your partner never discloses any part of your relationship to a potential partner as there are some people who are not into being in that type of position.
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Depending on what you are into, you could be at home and finding yourself very turned on by your partner out on a date with someone else, or you can be involved by watching what you partner is doing.
Just be sure that you are doing what you are comfortable.