Any reason why a male and female mouse shouldn't get along? I have them in a 40 gallon tank, so there's plenty of room. I got them at around the same time, about a month ago, and they used to be fine with each other and cuddle at night. Now he's chasing her around, squeaking, and backing her into corners. She squeaks, and stands up on her hind legs and tries to push him away with her front legs. I tried to look for an answer online, but everything I've seen says only two males and two females should fight, not a male and a female.
Here are some pictures, just because
This is the brindle male, Triscuit
And this is the black and white female, Cookie
I also have these two, in another cage. The black one is the male, Miko, and the yellow one is the female, Sahara.