Older men in their mid 30s usually develop some curiosity for a youngee breedable girl.
In that aspect Jackie was way over the top, Star shouodn't even be considered as Marco's adult necesities should automatically remove her from the list, she is clearly out of the parameters.
I'm not talking shit, ok? It's something psychological and studied for years, is not like they go for underage, but look for well developed teen girls due to a mating/breeding factor, but 90% of the time or so they just feel attracted but don't do anything other than look with interest due to knowing it's not exactly right for society's standards.
Dr. Marco Phd should have known this and be portrayed a lot more active with Jackie, flirty and perhaps even a lot more active in their relationship, it would have been cool.