I've seen suggestions elsewhere that depending on the intensity of an "incorrect" belief it could be considered delusional, but I have no idea how that line would be drawn.

I can't tell you how to get those thoughts out of your head, but I can tell you how I banished them from mine. First, I know I'm a million times better than my hubby's ex, no matter how screwed up I am, because I am good to him and for him, and she wasn't. So that one's easy. I'm clearly superior.

But I also know that I don't compare very well to the girlfriend he had just before me: she double-majored math/physics in 3 years with a 4.0 and got a high-paying job and bought a house within a year of graduating. Me? I barely made it through my math degree in the usual 4 years, struggled to get passing grades in several classes largely due to undiagnosed bipolar and ADHD (despite taking college-level math courses in HS and being a valedictorian with a perfect GPA), was wildly emotionally unstable at the time, and got a job as an AmeriCorps volunteer when I graduated (read: extremely low income, on food stamps, etc.) with no real career plans or ambitions at the time, or for several years thereafter. But she rejected him (after he'd bought a ring but before he'd proposed) and he seems to have very much gotten over that with 12 years of my undying adoration. So I don't worry about it. Again, I'm clearly the superior player because I could give him something she obviously couldn't.

Yeah, I'm a real pain. A lot of the time. But I am utterly confident that my better qualities outweigh all the craziness. My husband and I have a very strong relationship, and I completely trust him. It makes me more vulnerable, but it also means that I'm not subject to this particular flavor of insecurity (just several others...)