So, your actual problem is the legal expense and legal hassles involved in divorce?
Many/most of these are to do with the painful untangling of shared resources and responsibilities that come from sharing a life and resources. Marriage simplifies many things for two people - ‘we own this thing together’ becomes much simpler with marriage. The legal process of negotiating whether 20 or 40 or 50% of the house belongs to partner A is what tends to cause the pain.
Firstly, of course many people cohabit very happily for a lifetime, there’s no requirement to get married. They settle their affairs with bespoke agreements property contracts and wills. It works fine for them - it’s just a bit more complex than the standard package that marriage presents , but not a real problem.
Don’t want marriage, but quite fancy the tax benefits? In the UK you can opt for a Civil Partnerships which handles most of the outliers https://en.wikipedia.org/wiki/Civil_partnership_in_the_United_Kingdom
Bottom line -for people who want to get married, there’s marriage. For people who want to formally merge most of their financial affairs and tax obligations, there is civil partnership, for everyone else, there are bespoke legal and financial arrangements and contracts.
No compulsion, no loss of autonomy (other than mutually agreed) and certainly no slavery.
Good, eh?