Sorry looking buddleja (No replies)

Hello, newbie forum member here. I have a very sad looking buddleja at the moment. Bought from T&M last year and it did well. It's planted in a fairly large container, was looking good until a about a month ago and I noticed that it the plant was beginning to loose its leaves and looking all 'stalky'. I was watering all my containers, then when it looked worse I wondered if i might have been giving the plant too much water so stopped  (read that the roots could rot). Well now it looks awful no sign of flowers at all, some leaves are curling up and the odd one has brown patches on. Spider mite is around but when I've checked the plant i can't see any. Help! is this beyond saving? not sure what's happened or what to do for the best.