Suder was great, but he was only in three episodes. Jonas never made much sense. I mean, he doesn't like the way the Captain is going about doing things, so his solution is to betray everyone and side with the one Cardassian spy in the quadrant?
Seska used sex to manipulate and control men.
That she was Cardassian probably turned him on more.
That she was an evil Cardassian trying to destroy him probably turned Michael on relentlessly.
As with Neelix, they both left because no one on the ship was putting out.