My advice: find the excitement from within the marriage or get out of it. It takes effort to make sure you get the excitement out of your M but swinging/open relationships are generally doomed for disaster. You are initially excited by it because someone else either finds what you have as desirable (therefore it's a compliment to you) OR because there's the thrill of a chase or something illicit occurring. Also realize that there is a natural decline in sexual response and desire in men over time due to age and decline in testosterone levels. Simply going through a period of "lukewarm" sex isn't a good enough reason to me to expose an M to the hazards of such a situation. You haven't said how long this period has been, but what's hampering you from spicing up between the two of you without a third party involved? Is it because you may be wondering about your own orientation or aging or something else?
Personally, I would never get involved in something like this. I was bit hard by this though by my ex who not only had an affair with a bisexual woman but also participated in the threesomes and partners swaps with her. When I learned about what my ex was involved in, it totally disgusted me so perhaps that is coloring my response. (Remember Elizabeth Edward's quote about puking? I puked probably for 3 or 4 months solid.) But think of the possible emotional enmeshments that can occur and the threats of any STDs that can arise out of it. The alone should make you reconsider IMHO. Plus just my personal observation is that often times promiscuous behavior (my definition) is a mask for underlying issues that you haven't dealt with yet. Substitute sex for booze or pills or gambling. All can have a rather addictive component to them that can let you avoid the deeper issues.
My ex was completely screwed up by this situation and honestly, I couldn't stand the thought of him after learning all I had about what occurred.
Have you two considered a good marital therapist as well as individual T? Also I don't think it would be possible to have a solid, monogomous marriage should you really believe you are bi.
From all that I've read and learned having to go through the after math of divorcing someone who seemed to have been a secretive sex addict with the OW he chose, it seems to me that "open relationships" aren't really open. Think about this: there seemed to be a lot of rules attached to the situation (what you can do, what you can't do); that one partner does it simply to keep the other partner in the relationships (and the other isn't always happy about it); other emotional attachments occur that royally screw up the M; and the consistent lack of boundaries in such an arrangement lead to complete distrust and emotional instability with both partners.
