Yeah, it was pretty much the same (although it was kind of weird in the week or two following after the first couple times) -- which is to say it (that particular relationship) was fun (at times), but not healthy overall; on the surface, we were just more open to 3somes -- including FFM; we eventually split because we didn't know how to treat eachother... I do have to admit though, all of this happened on the downswing of the relationship (the last year or so)...
The impetus though, the actual straw that broke the back, was indeed a friend's involvement in a 3some -- things got emotional, lines were blurred, love was split between two people vs. one, yadda, yadda, yadda... One thing I strongly believe, 3somes are fun, but if you are going to do it, don't include a friend... unless you want an extra in your relationship...
We made some mistakes going into it -- we didn't talk about what was acceptable, what wasn't -- we didn't talk about "safewords" to stop the action if it became too much for one person to handle -- we didn't talk about who we should include, who we shouldn't... We just kind of got the idea and went with it, and once it was done, it was easy to do again without thinking too much into it... or how it would effect us as a couple...
And the thing about these things, is that the reality may differ greatly from what your fantasy of the event is... Human emotions can be a pretty fragile thing, and no matter what you say or agree to beforehand, things can be different once you're right there...