it could be winter! i know a member on here who does light therapy with her dogs because the lack of sunlight in the winter really gets to them- i know it is just horribly cold but i think you are getting a warm spell- i'd try taking him out on his own- no puppy- for walks and see if the sun light and one on one time help. Also- you are right- he isn't a puppy anymore- and probably at first his new friend was fun- but gosh darn it she just isn't going away
she is probably a bit much for him now- until she settles down.