I have found that my puppy (now 1 year-old) didn't ever like being around a lot of other dogs at one time. He seems much calmer around other dogs one-on-one. However, the exception to this rule is other Cavaliers. He loves being around his own kind... I think it helps that they as a breed tend to be calmer and less likely to jump at or on him, which he absolutely hates.
I still try and take him to the dog park on occasion, but he rarely strays far from me, preferring to stay at my feet if other dogs approach him.
Jelly Bean- 6yr Blenheim male