Hello,
Firstly, while using Bootcamp allows you to play The Sims 4 until they decide to release a Mac version, its not a perfect scenario to be playing the game in, and may cause problems that are much harder to fix, if fixable at all.
- Have you tried updating your graphics drivers?
- Do you receive any error messages after crashing?
If those do not solve your issue, you can try the fix in the following thread (courtesy of @EA_David)
http://answers.ea.com/t5/The-Sims-4/Sims-4-crashing-issues/td-p/3453033
I hope this helps and keep simming,
Cody