Democrats like to portray the Party as progressive, but progressivism is really just window dressing for the Democratic party. They like that progressive ideas get them followers, and sometimes a few progressives get elected (often opposed by their own party), but in general the party is Center Right with some moderate trappings.
Which is why it is so ineffective. This is by design.
Monogamy isn’t actually practiced by most of humanity. The existence of STIs that have evolved in the human population is ample enough evidence of that. STIs simply wouldn’t exist if monogamy was actually the norm. People may find it easier at times to pair off for sexual activity, but if monogamy was the norm then there wouldn’t be any opportunity for STIs to thrive.
The prevalence of paired relationships in many countries has to do with laws, taxes, and health benefits. (US perspective here) Many US states make it impossible for people in poly relationships to have and raise kids together. Those US states that don’t make it legally impossible make things difficult. Even for people in poly relationships without kids, there are issues of health care and access to family members in hospital and care settings, etc. All of this is a lot of extra effort that many people just aren’t willing to deal with, even if they wanted to be in a poly relationship.
From a purely mechanical perspective, human genitalia are physically evolved for multiple partners (simultaneous or serial). Species that are evolved for monogamy have very very different sexual organs.
There are programs out there (varies by state and county) which will allow you to be paid as a caregiver for your mom. That should alleviate some of the strain of caring. There are also services out there for in house caregiving assistance, which is lower cost than a care home.
County health agency should also be able to provide information on how to get your mom on disability, which opens up a wide range of program options.
Best to contact your county health agency for more information. They will have the scoop on your best local options.