1. Imagine if you were in his situation and it was your sister who had a mental disorder? Would you not want your husband to take care of her?
2. BPD is usually diagnosed in early/mid 20s. So consider if they really hid this info from you or it the diagnosis happened later.
3. A marriage means your responsibilities are his and his are yours. You both need to adjust your attitude, or this marriage wont last damaging the both of you seriously.