Lesbianism isn't forbidden in Islam is it?
Believe so. There's verses in the Quran about men lying with men and it being transgressive. Of course there's nothing about women lying with women, so feel free to assume that means it's allowed.

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YUSUFALI: "For ye practise your lusts on men in preference to women : ye are indeed a people transgressing beyond bounds."
PICKTHAL: Lo! ye come with lust unto men instead of women. Nay, but ye are wanton folk.
SHAKIR: Most surely you come to males in lust besides females; nay you are an extravagant people.
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YUSUFALI: "Of all the creatures in the world, will ye approach males,
026.166
YUSUFALI: "And leave those whom Allah has created for you to be your mates? Nay, ye are a people transgressing (all limits)!"
Theres hadiths and stuff too.