lpkR09,

I get that this is something significant between him and his friend/your sister.  I assume you have already told him that your parents are OK with you two.

I am uncomfortable how it sounds he is putting this sister disapproval issue on your shoulders by saying it will affect the relationship between him and you in the future.  In a not-so-subtle way, he is offloading the responsibility of “fixing” this onto you rather than taking ownership.

Again, a red flag in my eyes.

Mark