My boyfriend have physical relation with my elder sister

I know this is not what u want to hear but my honest opinion is that u should leave him because obviously he doesn't care about u or he wouldn't have been cheating on u with your sister all this time. I'm sorry and I'm not tryin to be mean and this is just my opinion and I really hope everything works out for u.

He's been cheating on you for two years with your sister... Why would you even consider marrying a man who can't keep his penis in his pants. He had the audacity to ask her TWICE. Do you honestly think that she's the only person he's been doing? Honestly, if I were you, I'd wish them the best of luck and leave them together. Because later on when you catch him cheating again, he's going to tell you that you shouldn't be surprised because you've already caught him before.

Neither he nor your sister has any respect for you, give both of them the boot.