I am in love with a non-Muslim

Urgent concern About My Sister. She is 18 and has fallen in love with a 16yr old non Muslim.. Asalamalaikum Everyonei.. I used to visit a chatroom and I had met a girl over there whom I consider to be my SISTER. She is 18 right now and The problem is that she had met a 16 year old boy in another chatroom who happens to be a non Muslim. The boy has fallen in love with the girl and now my sister has also fallen badly in love with the guy. She happens to be a very emotional girl and if I would explain her to quit talking to that guy she won’t do that as she does not like to break others heart. Also the boy has become mad and says that he’ill die if she leaves him. The case is the same with my sister as she is emotional she tried to explain to him that we aren’t doing the right thing but to no extend they both seem to understand. The boy is good in making her laugh and cheer her up which has resulted in the affection from my sister going up. I have advised my sister to be reserved with boys a lot of times in the past but she never listens and I am not able to keep control over her as we live in different cities. I fear if I pressurise her to quit talking to the boy either she’ll get depressed and end up doing something wrong, even committing suicide or the boy may end up committing suicide. I see no other way than leaving the matter up to Allah and pray to him to do whatever is best for my sister in this world and akhirah. May Allah guide us all and do whatever is in Haq. Please advise on what could we do and it’s a sincere request to pray to Allah that he may do whatever is best…please Advise