I’m sorry to laugh at your predicament, but it is rather humorous. I’ll make it up to you by trying to help. If you’ve decided to pick up a sword, then you really need to bite the bullet and go Combat. It’s an easier spec to level with, especially if you’re questing (no tank to really keep the mobs off you, unless you let your wife tank them, but if she’s doing that she’s doing more damage than you are). Assassination builds rely on Mutilate for their damage, and you don’t have the talent points for that yet. A question for you is also what poisons you are using on your weapons, as that is a large part of rogue damage.
I know you don’t want to go Combat, but it is probably the best build to level with, and if you really want to out-DPS your wife at those levels using a sword in a Combat build will be your best bet. Also, if you’re switching your weapons, then you lose a GCD between your Ambush and your next ability. I would suggest saving Ambush for instances, and just using Sinister Strike to build Combo Points, keeping Slice and Dice up at all costs, and using whatever finishers you have available to you after that (Eviscerate, most likely). If you plan on sticking with Assassination, then I suggest you get rid of your expensive sword and get a dagger again. Always use Deadly/Instant Poison and just wait until you can use Mutilate, as it’s amazing. Mutilate to build CPs, keep up SnD, and finish with Envenom. Good luck!

