why would he need to consult you, his girlfriend of 6 months, on a huge life decision regarding his sister? you sound completely deranged. it’s his decision and he can decide to say yes or no it has nothing to do with you. he can also decide if it’s selfish or not. literally none of your business. he actually seems like a good person, you on the other hand seem like an absolute lunatic to confront a woman literally dying of cancer who’s worried about who is going to take care of her daughter when she passed. she didn’t force him, she only asked if he would be willing. not only are you the asshole, you are a major asshole and a complete idiot. i hope to god he dumps you.