First, my sister and that boy fall in love with a boy at the same time, unless this boy is excellent and can be liked by two people, and these two people are sisters, which means that this boy is very lucky. No matter what the result is, I will be very happy, because he chose me, we are lovers, he chose his sister, and we are relatives. If we make this choice, it may be difficult. I will probably choose to be my sister, because I have a good relationship with my sister, and I will give this boy to my sister. Because I think affection is more important than love, so I will fulfill my sister, because my sister is very kind to me and takes care of me, so I also want to take care of my sister.
Second, my sister and I compete fairly. It is selfish to give boys the choice for love. Although my sister and I have a good relationship and she has given me a lot of care, I will not let go in the face of love. Some people will live forever if they miss it. My sister and I fell in love with this boy at the same time, which shows that this boy is really kind and excellent. Therefore, I can make everything else, only love. I will compete fairly with my sister. I will discuss it with my sister. I will give the boy a choice. If that boy chooses his sister, I will bless them. I didn't suffer, so he is my brother-in-law. If that boy chooses me, this is our fate, so I will cherish it. Boys will stay with whoever they like, and the other party will silently bless them, and so will my sister and I.
To sum up, this probability is very small in daily life. If it really happens, I believe everyone will handle their relationship well in a short time. Don't hurt your family because of love. Being a family member is the most important thing.