The problem is WINE has to reserve RAM so D3D and Windows does not call into a memory-space that they do not understand. Crossover is bad at removing old and unused data in RAM and with updates has become more and more unwieldy.
Two ways to fix the problem is to lower the texture and model settings and sound quality. Then you can troubleshoot to settings that get you to long enough play time without losing to much quality. Another fix would be downgrading your version of CXGames to 7.1, but be warned there was major fixes to Steam GUI support with the 7.2.1 version.