This title made me think this was a pact lmao. Instead of something that was kinda wholesome it's this nightmare of a situation.
Tbh idrk what kinda headspace ur in. Do what you feel you have to do. Don't stress about reactions etc, just make sure you get the death you deserve. Idk if u feel like you want her to see your body, or are capable of ctbing without being stopped.
My opinion, go find a hotel, book it for one night, and do it there. Preferably nothing loud to not draw attention, but whatever method just do it properly. That way, your gf won't have to immediately see body, you won't be stopped, and you won't be reported missing for a few days if not weeks. That missing report in truth is gonna devastate her more than anything. We need closure as humans.
If you fail idk what will happen in terms of ur gf. Ur guess would be better than mine.