Totally. What makes sense is to have a discussion about it and come to an agreement. Whatever arrangement that feels fair for both of you. You two have an arrangement that works for both of you and you’re both OK with it.

On the other hand just because you two are together doesn’t mean he’s automatically entitled to you paying 90%. That just happens to be something you both landed on and you’re clearly OK with it. Not everyone will be and it’s unfair to expect them to be ok with it.

I don’t think it’s unethical for your partner to chip in. Lying about it on the other hand is.