In the previous chapter, when Seju broke down, it didn't seem to me that she was telling the world how much she loved Sumin, but how bad a fubar life she's in. That's why I think what she really needs is just a friend who she can call a family. And I don't think her actions totally shut Nammi out. I think Nammi and Seju got a bit closer by now. Anyway, I don't say she will move on with someone, I think she will move on by her own.
In real life, you can let go of someone you love, and you are happy with this decision of yours, and you are happy when that person is happy, and your decision is totally commendable/honorable. I have no idea if there are many people who would honor Seju dying as they think it shows her one and only love for Sumin. But I believe there are people out there, such as me, who wouldn't honor her at all since we think that her dying is more like a way to escape from her sorrowful life caused by her family.
Someone here said all they want to see is a Seju's smiling face, a genuine one. Just so do I. Seju dying is really worst of the worst scenario to us, at least to me.