Welcome to BB Forums. I'm really glad that you were able to post your story here. It takes great courage and bravery to be able to share your feelings and troubles.
It must be really tough for you, to have your parents disapproved of you to be who you truly feel you are. To be the eldest of that family and be a role model to your younger siblings like what your parents (or any Asian house hold family) expect of you, that is a lot of burden and responsibility that your parents have imposed onto you. Whenever you can't meet those responsibilities and expectations from your parents, you feel like a complete and utter failure. I'm really sorry to hear about that.
As much as our parents wish for the best of us, and they have this perfect idealization of who they want us to be. We must understand that they've lived through their years with countless numbers of experiences and events that carved them into the person that they are today. By recognizing that, we can learn to accept their flaws, and accept the sympathy that we have for them for not being able to have the child that they've expected from you. Living a life of only meeting the expectations of others, would just mean we're being dishonest to ourselves.
But if I may say, you've done really well thus far for yourself, and found an amazing partner throughout your journey and living a happy life together with them. And so long as you're living a happy life with your partner, I feel that's all you need to do to show your parents that you don't have to meet their expectations in order for yourself to be happy. They may not be acceptable of your sexuality for now, but if you continue displaying how you're living a happy life, and the life that you want, perhaps over time they will learn to accept you for who you are.
Live true to yourself, and if you choose to let them know the truth, know that their anger and disappointment is not something you are responsible for, or can control. It is something that your parents will have to manage themselves, and learn to accept. Their expectations of you, is for them to manage, because only you know what you truly want out of your own life, and that is the only expectation we should be managing ourselves.
Stay strong my friend, you are not alone, and always happy to chat with you more.