I'll also offer a perspective here, which is that the jealousy that comes from a partner sleeping with someone else is often tied to fear of losing them. If there's no fear of losing them (as there isn't in this case), some people might be significantly less jealous.
I understand your point, but Adrian seems relatively phobic with respect to the Watch. It's not like he tries to understand or master it; I don't understand why he'd be so confident in it. Plus, you know, he's got a history of being abandoned by lovers (or at least *a* lover, though it was a big deal). Perhaps he's overcompensating the other way, instead of being controlling and jealous he's thinking that Erin needs to be with other people to be satisfied.
- Adrian is spread pretty thin these days, and the harem has a schedule. If Erin needs to charge up more quickly than that schedule permits, and doesn't want to tell Adrian about her need, then banging other guys might be the best option available.
It's unclear if that's even what's going on. There's too much left undefined with respect to magic to know if she's doing anything other than just enjoying the sex she's having.
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- Erin pronounced herself broken and in need of magical help in #646, immediately after sleeping with Adrian for the first time post-Jakobite. She hasn't slept with him since then. Perhaps there's something about the breakage that's tied to Adrian and means she has to get the energy she needs from others instead.
That's interesting. Maybe she's trying to distance herself from him, as best she can. [/list]