Websites of medication manufacturers are usually one of the most reliable online sources of information about the product in question. Other sites may give you false information, but the manufacturer's information is researched carefully and bound to be correct. It is interesting that the word "libido" doesn't appear anywhere on NuvaRing's informational page on side effects.
They mention blood clots, high blood pressure, and other unpleasant stuff (particularly if you smoke, so don't smoke while using the NuvaRing!), but apparently users' sex life is not mentioned. Weird, for a birth control method :).
Online forums do reveal that women using this birth control method complain about libido changes with some frequency. There may be no science behind that, so don't take it as more than anecdotal evidence, but if you don't feel like having sex while on the NuvaRing you would not be the first one.
Discuss it with your doctor if it happens to you, because it may very well be that libido changes are very much temporary while you get used to the vaginal ring. On a related note, did you know that men can be allergic to the NuvaRing? I hate to even think about the possible results of such an allergy, but you may want to look this up before you commit to this contraceptive method.