The answer to your question Fuse is No. In our experience we have not found any marital difficulties with the "experienced" soft swap couples we play with. In fact, we have found the opposite to be the case...our experiences with these couples have been positive like westernswing, chiccup, and Fuse described. I don't think the experienced, well adjusted, enthusiastic soft swing couple is that rare either ...but only speaking from our on premise club and swinger resort experiences(we have never done the online dating scene..maybe it is different there?) I guess there is a big mystery for some couples why a couple in the lifestyle for many years chooses not to full swap...just ask them, and I'm sure you will find that the green monster is NOT their reason.
xoxo,
Allie
-we play with all levels of swing couples(mostly full swap cpls) and put our experiences on our podcast if you are interested.