What can I do to stop this?

[winsock]

And how is he not screwing me over for the pursuit of his own goals by wasting my time in a dungeon I don't want to do?

If you dont want to do dungeons in the roulette, dont use the roulette. You're selfish because you're going into it knowing you have the possibly of not getting what you want, and screwing ppl over if you dont get your way.
In the OP's scenario, he is queuing for dungeons other ppl are also queuing for or that is contained in roulettes that ppl are queuing for.

In short, when you queue roulette, you consent to being available for any possible duty within that roulette. Crying and screwing over the rest of your party when you dont get the outcome you wanted from a "roulette" is childish and selfish.