What Do I Say to My Sister?

Like the title says, I need help with how I should/shouldn't approach my sister.

So my sister has been dating this guy she met online for about two years now. She says she's in love and happy in the relationship, and she says she wants to get married right after she graduates college (she's only 21). My problem is that she's extremely young to get married and she's had issues with mental illness in the past. Recently, she came over to visit my family and myself and she said that her boyfriend's parents had said they wanted my sister to live with her boyfriend at their house-which is fifty minutes away from her school. My sister and her boyfriend were planning on living together next year, but his parents wanted him to save money, even though he already has a job, and live at home for another year. When my sister told my family this, she seemed very certain that she didn't want to live at her boyfriend's parents for a year because she would have to spend an incredible amount of money on gas. However, my sister left extremely early, and ended up crying while she was driving saying that my family didn't like her boyfriend which we never once indicated. I guess at some point my sister told her boyfriend's parents that she didn't think living with them was logical, and the boyfriend's mom ended up saying how disappointed she was in my sister. The next day, my sister attempted to take her life because she thought everyone was disappointed with her. Luckily my sister didn't end up taking her life.

I was kind of pissed at her boyfriend because I knew my sister struggled with mental illness in the past and I would ask her how she was frequently, but she would always tell me she was fine. The only person she truly confides in is her boyfriend. He waited until he knew my sister was trying to take her one life to tell my family that my sister was struggling.

Now, my sister is saying that she wants to get married and wants to move across the country with her boyfriend. The boyfriend's mom has been pressuring the him to propose and it pisses me off. My sister is twenty one years old and and needs to be focusing on herself and her mental health. My parents seem completely fine with the wedding and her moving despite all this. I don't know what to do. I know this may seem like jealousy because my sister is leaving but I'm concerned for her safety. She doesn't tell me what's going on with her when I ask and let her know I'm there for her. My parents don't believe in mental illness, so they're not going to say anything.

Should I do anything about the situation?