One thing that will keep this from becoming a "Harem" series is the "Harem" themselves. In a "Harem" series, most of the comedy revolves around the girls vyeing for the guy's affections. Here, Jean has a life; Sarah is more interested in getting the Wuff under control than in Peter; and only Rebecca seems to be interested in Peter
himself, and there are a lot of questions as to "what for?"
While (if they are all going to the same college) Jean will be looking for Mister "Right for now",

Sarah will probably just take Wolfsbane on "those days of the month" when she has "Wolf Problems" and may
never deliberately shift into Ms. SuperMax (Sarah-the-Werewolf) even with Sarah firmly in control. I suspect that she will think "I had sex with Peter
once, and
this happened.

That's quite enough: pass the equations, please."

I don't think she will consider the number of times that the Wuff has had sex with Peter as relevant; "I wasn't in control, therefore it didn't happen." Peter will be taking a lot of cold showers. The "mated for life" that the pack imposed won't be enforcable outside of the pack's territory.
As to Rebecca,

she may actually have some feeling for Peter, as she was willing to "call him out" at that long-ago (here) Howl, where her father would be under the control of Sheriff Con, as well as the other Elders of the pack. All that bluster might be her concept of delicately approaching Peter--and remember, on page one he was coming from what he called a "confrontation" with her when the Aminal Control people started the whole story. Perhaps she was telling him that she wanted him as a mate, which would make most males of that age run for safety, and in Peter's case, shift. Fact is, 'Becca is about as tactful as an M-1 Abrahms Main Battle Tank, courtesy of her daddy's peculiar method of Parenting.

That would fit her actions that happened later on, as well.
Of course, I'm probably wrong on this...

but it does bear consideration.
As for Peter, our cringing protagonist;
"Duck Season" has nothing to do with hunting: it's a way of life

KMacK...
"You don't have to be invisible when everybody is looking the wrong way..."
Writing the series "Wulfen Blood"... getting ready for publication.