-Nades: I am trying to install part 2 and it's asking me what I want to open the file with. No idea what I'm doing. Please help.
What happened when you ran the first part? Did it install the game?
There is no "second" (or third for that matter) part that you need to run separately. The "part 2 of 3" and "part 3 of 3" .bin files that you downloaded too are data files that the installer (the "part 1 of 3") uses for installing the game. The game installer is divided into three parts due to the size so that it is easier to download, copy to an USB stick and whatever.
You download all three to the same directory, and the run only the first part (the .exe file, the application).
EDIT: And the reason why Windows asks what to do with the file you try to run (part 2 of 3, or part 3 of 3) is because it doesn't know what the ".bin" files are for, and which application should be associated with them. If you have e.g. some CD-R burning software or the VLC video player installed, then it might be Windows thinks (incorrectly) that you'd want to use .bin files with those applications, when you double-click on a .bin file. CD burning software and some video players (like VLC) associate .bin files with themselves so that they would be the default apps for disc images (which may have the .bin suffix as well).
When you reinstalled it with Galaxy, did it redownload the whole game? I wonder now if you have the game installed twice, once with the offline installer, and then with Galaxy. Or did Galaxy notice your offline installation and import it automatically?
As for your game running problems, either contact the GOG support, and/or read the Mefal of Honor subforum in case someone had the same problem as you and got it fixed easily.
https://www.gog.com/forum/medal_of_honor_series#1498075081