I share your pain. Unlike you, I didn't realize the debt my partner had until we moved in together. Prior to that there was a lot of smoke and mirrors when we talked about finances. I am currently subsidizing his debt (he pays a few $ a month toward household expenses. Rough 1/4 of the real cost). I have to remind him every month, and he only grudgingly transfers the money.
The real problem is he has gotten used to me paying more because I made more. When I ask him to pay, he bristles. Its an effort to get any $ out of him, yet he spends plenty of bucks on what he wants.
Now I've lost my job (company closed) and his attitude hasn't changed a bit. He still expects me to pay because I have a "bundle" of money set aside for retirement. He knows it would provide only 35K/yr, but that doesn't seem to matter.
It should be no surprise that we are breaking up. I think I'm done with the whole partner-stuff. I have a very active social life, love my friends and value my alone time.
Good luck to you - but I would cut my losses and consider the mortgage you'll be paying alone as an asset for your retirement rather than an unexpected burden.