When do men stop thinking "MY" money and start thinking "OUR" money?

I've been living with my boyfriend for over 6 months now, and he earns more than me but we still share things 50/50 (which was admittedly my idea because I assumed after time he would grow up and start to pay a bigger share).

I drop hints how things might be tight this week etc, but he is still very selfish with his money, and I've even mentioned to him we should have combined incomes and put all our money into one account but he doesn't like the idea, said that's for married couples.
When do men stop thinking "MY" money and start thinking "OUR" money?
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