Autumn Asked: Why aren’t my rats pregnant yet?

This is a bit of a weird question so here's the backstory:
I have three female rats. I was at a pet store and saw a little boy Dumbo rat about to be fed to a snake. He was too cute, he looks like a badger, and I asked to hold him first. He cuddled up and chilled. He was about 9 weeks old and I took him home. Now, the place I got him from ONLY gets rats from a pure line, from a breeder in Dallas, Texas (3 hours north of me). He was sold to me with a health guarantee and proof of his good line. So he is thoroughly healthy, as are my three girls (one Hooded Fancy, one Velvetine Dumbo, and one Siamese Dumbo)
I have 4 cages and a carrier, but for now I've kept them all in the same cage and keep my eye on them, and at night I separate Loki, the boy.
I have yet to see Loki even TRY to mate with any of the girls and I've had him over a month, except the Siamese Dumbo, but from what I've seen he hasn't succeeded. None of the girls are pregnant, either (I don't think), so it's a bit strange to me, is there any reason this could be happening?
I'm getting him neutered next month. :] I just had to get the money saved up because I'm PCSing with my husband (and taking my ratties with me).
I'm definitely glad for no pregnancies yet, even though my husband wanted to feed the pinkies to his gecko.
But yeah, advice?

ALSO, Loki and my Siamese, Raichu, have this strange attachment and will NOT be separated. I'vve always heard rats do not breed for life so this is a bit confusing. She's the only one I've seen him even try to mate with. They share food and treats, he brings her food, they groom each other, they cuddle and they freak out if I separate them. Could they be life mates? It's very cute, and with the lack of interest shown in my other two girls, it seems probable.