I really want to buy this game but I need to be sure it doesn't crash on me. I played the free version (the website) but it kept crashing so I downloaded the demo and ran it all night and it hasn't crashed
should I buy the game?
Yes you should buy it.
If the demo on this page works for you then you should be fine.
You can just download the demo from this page? Test that out and see if it will crash on you before committing to buy. That's what demos are for.