Need Help on Life

Ok, this is my first ever post/contribution on this platform. I am seeking life advice from other adults who have shared similar experiences and what you decided, and how you think it has turned out.

Hello, I am a mom of three ranging from 15 to 7. I work 4 ten hour shifts and make what I consider OK money in a job I love. I also have a mother who is older and lives with me. My Oldest does not share the same Father as my youngest. My "Fiance" of 10 years and I share a home and have a "Ok" life with the kids. I am not without my own faults, however we have been circling the same subjects for 10 years and I feel no progress has been made on pretty big issues on my spouses part. I am torn between leaving and staying, I feel like my children are being negatively impacted by what os happening in the household that is and has been a toxic cycle. (No violence other than yelling, not between the adults.) I have threatened to leave numerous times and change would ocur and then not. 10 year cycle of this. The thing is I do love him but it's taking a toll on myself and I feel the kids, my partner has refused therapy, and anytime I express my concerns, shuts down and we forget it ever happened/is a problem until it's brought up again, just to be a cycle.... Also my partner keeps moving in random members of the family who DO NOT contribute much if at all, and I end up kicking them out, latest is his mom and I feel I cannot kick her out but I also cant live with her. My 7 and 9 year old dont even like her much and ask me why she is here and they dont want her here.... I am worried if I leave my kids won't have the same quality of life they are used too and it would be a larger financial burden and a TON harder to figure out how to completely do it on my own, he will not leave our rental home, so I would need to.... I am also unsure if I will be able to even find a place big enough for 5 people on my own, my thinking is maybe a cheap 2 bedroom with a yard... I could share a room with my daughter or just give my kids the bedrooms and sleep on a futon? I bought my mom a camper a while ago so hence the need of a yard. My mom cannot contribute much financially. Also if we share 50/50 custody do you still pay child support? I am the only one with income. Any advice on if I should stay? Keep living the cycle and hope my kids understand when they're older? Or leave and try and give them a healthier household?