The ending is batshit crazy but no worries we've seen crazier lesbians.
It's also deserved since Lily was the one jumping from one person to another and couldn't accept that Anna's love for her would not develop into a sexual relationship and also equating Dutchess's desire and manipulation of love.
Honestly, if we remove the pretty face filter here and imagine them to be like stock figures it'd be such an annoying plot to read. Although even with the filter Lily seems very dumb. I do realise that she's always been in her room in her father's mansion and never been in touch with worldly emotions but she's still so fucking dumb