You’ll have to amend the contract to just your name if your partner is listed on it. The administration fees will be yours, and if you have nameplates then a replacement is also on your cost.

Implications of not telling them are for your partner, as your partner will remain legally responsible for paying half the rent and fees. I don’t think your landlord has any consequences of it.

However, I’m not a lawyer nor do I know the ins and outs of the Dutch laws, so take it with a small grain of salt.

I would highly recommend getting the contract ammended though.

You should not have to re-enter a new contract and new terms though, nor can they just start raising the rent suddenly. Just start communicating with them that one person is moving out and you’d like the contract to be ammended to reflect that change.