Would you stay in a relationship with someone that sufferers from Mental illness?

Basically they suffer from Bi polar depression or PTSD , they resemble DR Jekyll , Mr Hyde , They are sweet and caring to you for a little while, but then turn complete opposite on you and treat you like complete shit like a flip of a switch , saying vicious things to you and pretty much pushing you away like you are this horrible person all of a sudden?
Would you stay in a relationship with someone that sufferers from Mental illness?
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