She/he is in a mentally deficient state, and will be mentally retarded for the remainder of his/her life. They will need aid in almost every aspect of life that may seem arbitrary to some.
Do you still love them? [b]and why/why not?[/b]
And, for deeper thinking:
[spoiler]What if no one other than yourself and the other individual knew about the relationship?[/spoiler]
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I'd stay by them, because I want them to get them better... And even if they won't I'll hope, I still care about them because even if they not their whole self the human brain doesn't let go of feelings easily