I can't play multiplayer Terraria with anyone having steam version because gog updates it so late they always get new version by this time... Since a week there was only 1 day when we could play together when we had the same version and since steam auto updates and doesnt allow downgrading we cant play due to very late updates on gog

Why don't you buy it on Steam, to play with Steam users? The game is super cheap, and is great, it's totally worth it.