No, you can't.

First, even if you "scare" her off...there may be others (now or in the future). If he's bound and determined to cheat, he's going to cheat. Be it with this woman or another one he may find down the road. You can't fix your marriage by dealing with the other woman.

In my opinion, it doesn't sound like he wants to fix the marriage. I'm sorry but it's NOT all on you. That's crap. Marriage is a partnership. You definitely need to see someone.

If it were me, I would tell him that I found these pictures and confront him. Yes, I was wrong in the manner I obtained them, but I still found them. Two wrongs don't make a right but it's done. I'd tell him I'm seeking counseling to help me with my insecurities but if he doesn't make some sort of effort to save the marriage, I will assume he doesn't want to save the marriage.

That being said, don't make ultimatums that you aren't prepared to follow through on. Say it, mean it.

Lastly, find your own support system. Family, friends, folks here. You need that support right now. I'm sorry this is happening to you, but you will make it through.