Wait, so in the Ghilan'eth AU does Olwyn not have anyone else before she gets with Mythal? And does she take other lovers afterwards, like Mythal does? How does she feel about Mythal's lovers? Does Mythal get jealous of Olwyn’s, if she has them?
No worries, anon, Olwyn wasn't pining away before Mythal came along in the Ghilan'eth AU.
Her grandnanae Melarue DOES work in the Pleasure District after all, and it's the place where their rebellion ran most of its intelligence network from. So Olwyn visited there quite often, and sometimes it wasn't just for business. I've mentioned in the Cullen in Janiculum AU that she's had a few partners: Desire and Eagerness, most notably, and also one of Ghilan'nain's halla tenders. It can be assumed that those partners were ones she also had in the Ghilan'eth AU, and there is also Delsaran, one of Melarue's apprentices, who has only briefly been mentioned but will be appearing more with Ghilan'eth.
If Olwyn has a serious partner, she tends to take that partner's wishes into account. So with someone like Mythal, who we know also had other lovers throughout the years, she'd feel less worried about taking her own. That being said, they would be casual relationships.
In regards to jealousy, Olwyn's not the possessive type. There is a few years, after the birth of the twins, that she finds herself oddly covetous, but most of the time she's really just battling with the fact that she cares deeply for Mythal and Mythal is, in fact, the person the rebellion is fighting against. There is a lot to digest for her and she's just trying to work through that. XD
On whether or not Mythal get's jealous of Olwyn's lovers, I'll leave that up to @feynites to elaborate on, but my assumption is that no, she doesn't get particularly jealous, and only would make a comment if Olwyn were to suddenly declare she was going to marry one of them or have children with them, which is highly unlikely.