Ah, that classic WTF moment..."My partner suggested swinging, and I'm not sure how to react...", you hear this kind of thing all the time in the community, and I can promise you, at any given moment, there are tons of other couples who are in the exact same boat. It's almost a Swinger "right of passage" to go through this part of entering the lifestyle. At some point, someone has to bring it up, and feelings have to be felt before any kind of fun can be had.
What now? The first thing you do (or second, if you are like many couples and started an argument first) is CALM DOWN. Do not panic and do not get mad. Respect your partner for coming to you and being honest with their feelings. It takes A LOT of guts to suggest opening your marriage, especially in a society where monogamy is the norm and sexual relations outside of your relationship is frowned upon, worrying about the backlash you may receive from your partner can be incredibly tough.
Take a moment to consider a few things:
Your partner respects you and your feelings by being honest about their feelings.
They trust you enough to open up about their sexual fantasies.
They want the two of you to be actively involved in trying new things; they want to adventure WITH you.
So, we've calmed down a bit, yeah? Now it's time to consider pt.2!
Are you willing to engage in these fantasies?
Do you possibly share some of these same fantasies?
What are some things that would benefit YOU in the Lifestyle?
How could this benefit BOTH of you?
Once you've answered these questions, it's time to proceed! At this point, you're likely warming up to the idea of swinging, or at the very least considering it. So, how do we go about it?
First things first, you need to establish your ground rules. Rules and open communication are the cornerstone for any successful & healthy swinging relationship. Rules are what keep everyone comfortable and communication keeps everyone happy. Every couple's rules are different. No two swinging dynamics are EXACTLY alike, and what works for one couple, may not work for another, and that is 100% okay! Decide between the two of you what you would like to get out of the Lifestyle and what each of you are comfortable with. These rules are to be absolutely unbreakable. If you have an established rule and you break it, it could be the downfall of your relationship, so keep that in mind AT ALL TIMES.
Now, that's not to say that rules can't be re-worked or re-visited EVER, but re-visiting an established rule is something that should always be done long before considering changing your play time. Couples grow and rules change and exceptions are made all the time, but the key part to doing this is to openly discuss the matter and your reasoning BEFORE you're put in that situation. Rule changes and exceptions should never be made in the heat of the moment, as they usually lead to regret for both parties involved. Long story short, establish your rules & stick to them.