*mpf* OK, an example:
My husband stopped making payments on the loan after his separation from his ex because he no longer lived in the house. That was agreed upon with the ex. However, he was still listed on the loan. If his ex had also stopped making payments now, the bank would have gone after my husband again.
The bank didn’t care when only my husband’s ex paid, and the bank would have also not cared if my husband had paid instead of the ex. It didn’t matter whether the loan was taken out 50:50 or 20:80 or 30:70 or whatever.
The bank does not insist that a partner pays 50% if that is how it is set up.