Are you shutting down all non-essential programs (especially anti-virus) before starting the game? Firewalls have caused conflicts (generally on loading screens) and overlays from graphics tweaking/monitoring programs or chat programs have also caused issues.
If you check the Event Viewer, does that give an error code or 'Faulting Module' file name that might help identify the cause of the crash? - click Start (or WinKey-R or WinKey-W in Win 8), then type "event viewer" into the search box. in Windows 10, 'event' should bring up 'View event logs'. - after starting the Event Viewer, expand 'Windows Logs' in the left column and select 'Application' - in the center column, look for a recent error (maybe sort by Date and Time) for the game - check the information under the 'General' tab below the list of events, starting with "Faulting application name..."
If applicable, disable Steam cloud support either globally (in the client click on the Steam menu and select Settings, and then Cloud) or just for this game (in the library right click Divinity: Original Sin Enhanced Edition and select Properties, then switch to the Updates tab and check the Steam Cloud section).
Next, try browsing to the '..\Documents\Larian Studios' folder and rename the 'Divinity Original Sin Enhanced Edition' subfolder. This folder contains the saved games, configuration files and a level cache folder. Deleting or renaming it will get the game to recreate it on startup; playing the game from a different Windows user account would effectively do the same thing. With Steam cloud support enabled, Steam would just download the cloud copy of your existing profile. After that, start D:OS, create a new profile and see if you can start a new game and save/load. If that works, exit and then copy a couple saves from the renamed folder into the newly created profile's savegames_patch folder. If that lets you load the saves, move the rest of the saves over. If a new profile doesn't help, delete the new My Documents D:OS EE folder and rename the original back again.
Did your friend try hosting? You can email one or more saves (or a Dropbox or Google drive link, etc) to continue from any of the saves that you made, and still have. Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin Enhanced Edition\PlayerProfiles\<ProfileName>\Savegames_patch' folder.
