triad...all 3 people have a relationship together...in turn 4 total relationships (you with gf, gf with bf, you with bf and then the 3 way)
V...really just 2 couples, with one person being common...The point of the V would be you...your gf and you bf would each be a leg
The reason for labels...is labelling...makes things clear. My wife and I have been in a triad...it describes a different relationship than someone in a V...
how do you find someone who doesn't mind being considered second best?
That is a magical question....the chances are, you don't...but there are sometimes people out there, currently in primary relationships that don't mind having you as their secondary...
I have also seen on okc, the odd person quite simply explain they aren't interested in a primary relationship at all...they want to remain "single" while ethically dating a few people.
If you are looking for a 3rd wanting to commit to a long term triad as a secondary AND be monogamous to the triad/v...well...that would be an unfair expectation.