need to buy the game for each platform???

[hero1900]

maybe i am mistaken i check it when it long time ago
but thats what happen so it means i cant get it since i bought it from steam, which has only windows version.
okey thx i just get confused i check desura and saw that there is no promotion so i thought its only windows promotion, usually companies make that so i thought its windows offer.
thx

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finally so i need to buy it again if i want linux version, since i didnt buy it officially (or what so ever)??
thats what i can get from the unfocus replies. i just want an answer yes or no please no further thing. you can say i was stupid and i buy it on steam so do i need to buy it again for linux???