Demi Moore is still bitter over the breakup with Ashton Kutcher, and rightfully so. He left her for another woman, which is a big sting. In addition, it plays into Moore's fears as an older woman being left for a younger model. Kutcher's behavior with his girlfriend just puts salt into the wound for Moore.
On the one hand, Ashton Kutcher has moved on while Demi Moore is just a washed up and older actress trying to remain relevant. On the other hand, what did Moore expect? Kutcher is young and should be with people closer to his age. He and Mila Kunis had chemistry from their past on "That '70s Show." She should have seen that relationship coming.
Demi Moore sadly seems to have some emotional issues that causes her to seek our less than normal methods to help her function. However, I think that these things are not indicative of her break up with Ashton Kutcher. She probably doesn't like see him dating Mila Kunis, but who would?
No, Demi Moore is not still bitter over the breakup with Ashton Kutcher, because they appear to be quite amicable. No one will ever feel perfect after a breakup, but Moore has said positive things about Kutcher, and they appear to be working things out. Given the age difference, they both had to have known it would not last forever.
They are probably both fine in the long term, and are probably fine as is. Demi was significantly older, so she was both more experienced and also probably aware that the relationship would not have gone on forever with the much younger actor. They are both rich and famous, nobody is bitter.