That is my point. Janeway is a COMPLETE prude.. She keeps chakotays balls in a jar for 7 years because he's a pussy. (He's her fallback plan LOL)
She has had ample opportunity to bang tuvok (maybe she has)..
So here comes this alpha male Kashik and she is like "wow who knows when I'll get another chance for a one night stand.. PANTIES ARE DROPPING"
That bullshit about "holding out for mark" and her dear john letter as her closure is just typical chick logic. You notice how she arbitrarily changed her hair style and got more assertive WELL BEFORE THAT (season 4 i believe)
She was about to make out with that French magistrate guy in Prime Factors until Ensign Harry "Cockblocker" Kim decided he's rather interrupt and tell Janeway about the new tool he found than spend time with the chick who was all but throwing herself at him. That was in season one too, so... yeah "holding out for mark" logic rebuffed.