It sounds like your game is likely crashing from a lack of available memory. If you have added more assets recently, or if any mods or assets have updated, or if you got another DLC recently, that would increase how much memory the game uses, which would explain the crashing. But it doesn't have to be related to the game. An update to your operating system or any program that runs in the background could also do it. Or if you have less available harddisk space for your pagefile, then that could also do it.