Why is my friend suddenly talking about me getting married?

It's just something for her to contemplate since she isn't for certain going to get married before you do with her breakup of the boyfriend. Maybe she wants to see if you are a lesbian and don't know it? Perhaps she is getting out of her "it's complicated" relationship due to her desire to try a lesbian relationship with her best friend and now seems like a good time to try. It could be for many reasons.