Wits end with irresponsible parent

I’m hoping some can help as currently at my wits end with my irresponsible mum. So my mum is divorced from my dad and in her 50s they have been separated since I was a teenager so that’s 13+ years now. She has lived in our house rent free and never paid the mortgage or any household bills until we all turned 18 - my dad really looked after her but she is still so negative about him. He has even said she can live in the house for as long as she wants and he doesn’t want anything from her. I currently live at home and saving for a property with my boyfriend. I feel as though I have the weight of my childhood home on my shoulders, perhaps my cleaning standards are too high but I am forever coming home and cleaning up after everyone. My mum works late shifts sometimes which is fine, but on her days off I come home and she is sat at her computer. The computer is what I expect was the cause of my parents divorce, she lives on the thing - I have tried to tell her that she doesn’t have to live on there, and to be honest I’m not entirely sure what she does on there, she plays a lot of online bingo so I can only think she has some kind of addiction to this. She is irresponsible with money and will ask to borrow from me at Christmas and having to pay me back all throughout the following year, this causes issues between me and my partner. She ‘forgets’ To pay phone bills, and any actual issues which could potentially cause big problems she doesn’t want to sort it. Example being a company messed a direct debit up - completely their fault- she needs to call them and is refusing to do so, because it’s not her issue, I’m sorry but a unpaid bill is still your issue and a normal person in my eyes would resolve this. I am finding this situation extremely frustrating and I don’t know how else I can tell her she needs to start acting like an adult before I explode. I have tried talking to her and she just snaps back, automatically on the defensive. I really don’t want to have to pull my rent money but feel if this doesn’t end soon then I will have to find somewhere else to live, and it could potentially ruin my relationship with my mum.