Well,do you want another relationship?
Just because your wife is poly and has another relationship doesn't mean you have to. Sometimes the poly half of a couple encourages the 'lesser poly' half to coin a bad term to find another relationship so things are 'equal' or they can feel less guilt about having other relationships themselves. I have no idea if your wife is doing this - I have no way of telling. Think about that carefully.
Also, just like being gay (with a few exceptions!), there is no way to tell the polys from the monos down at the local grocery. How open you and your wife want to be - or perhas can be - is something to discuss.
And if you decide you want a relationship (or two!
) for yourself, OKC is a fine place to start. Many poly folks note somewhere in their profile that they are polyamorous and their spouse (if they have one knows). Some partnered folks link their profiles to their spouses or partners. Others just talk about non-exclusivity. You will have to feel your way around this issue.
And it is a good idea if you are totally new to the concept to read heavily in this forum. It will give you the lingo and you can start to see some of the common issues or problems that come up.
Good luck and welcome!