I have a problem with my two zebra finches.
Half a year ago the female in the pair sadly passed away. This left my male zebra finch alone. I chose to buy a new female to keep him company because I know that they are social animals.
At first they got on but he was always reluctant to let the female into his nest. Eventually I noticed that the female was plucking feathers from his head!!! So I split the two of them in separate cages to stop the abuse

Two months later I re-introduced the female and it didn't work out. The male was being really territorial and kept charging at her like a mad bull. So I kept them separated, with their cages closely beside each other.
Now whenever their cages are apart they scream for each other, but when they're in the same cage the male attacks the female. I don't know whether to return the female and get a new one but it's been 6 months and I think they've become 'friends'. It's really sad to see them separated without any contact, I want them to be together!
Is it because zebra finches are monogamous so my male will never accept a new partner?
The female also has a separate nest of her own in her cage, does the male think she's laying a clutch?
Would removing the female's nest solve the problem?
I would really appreciate it if anyone could help me with this dilemma. Sorry for all the writing

Thank you!! <333