Why on earth have you let him move in without understanding each other's finances?!
It's hard to understand exactly what the issue is here, because you don't actually say.
But I gather you've just discovered that he has more disposable income than you, and he's planning to use your generosity of living for peanuts at yours, to feather his personal nest via the buy to let, yes?
If so, he's taking the piss. You share the fruits of your labour with him, he should share his with you. And I wouldn't accept any "it's for our future" crap. You're just boyfriend and girlfriend. He could live of the fruits of your (past) labour in the rent free home, then walk away at any time with his nice buy to let.
Do not make the mistake of thinking that love is giving away your money.
The biggest thing that has me
is this line about him trying to keep you both happy. So - does this mean he's been lying to you, and is now trying to blame you for it?
FWIW, when my fiancé moves in with me, he'll pay no bills (Well, he says he's going to!) and he'll pocket all the income front renting out his place. We'll have a pre-nup, so I don't gain from his house at all (or him mine) if we split. But I'm happy with this because he earns less than me and we're absolutely transparent about finances. They are separate - but transparent.
It's OK to give a true partner your money. A boyfriend of just a year who has lied about his income and is using your money (in the form of subsidised housing) to turn a profit for himself - not so much.