Breeding Zebra Finches?

I have had my zebra finches for about month now, 1 male and 1 female. I got the male from my cousin because he didn't want him anymore and I got the female from a shop because I wanted babies. I have bred my cousin's male before and he had 3 adorable female babies, but the male's mate died after giving the babies to new families. So now I got another female and they were good for the first 2 weeks and sleeping together in their nest. I saw them mate a couple times, but lately the male has been plucking the females feathers, but they still get along. So why is the male doing that? And just recently I have noticed that they don't sleep in the nest anymore and they completely ignore it, but they still sleep together on a perch. What is going on? Anyone have a solution? Should I move the nest to a different spot or should I separate the couple completely even though they are doing fine except for the feather plucking?