And the garage isn't even technically connected to the house, theres a walkway that separates garage from front door
So leaving the garage door open would keep the residents of house safe from the gas?
I would certainly think so, because surely the majority of the CO would escape through the garage door, and would then just pass into the wider atmosphere.
If the garage isn't directly connected to the house, then having the garage door open might not even be necessary, but it all comes down to trying to judge, so there's always an element of guesswork to some degree, and perhaps it's best to play safe. Plus I don't know your house as well as you of course...
Based on what you've told me, I would think if you did have the garage door open as an extra precaution, then that would be more than sufficient, since you then have 2 protection factors - the open door, plus the separation of the garage from the house.
But again, I'm in no position to give guarantees, just my best guesses based on what you've told me.
It still comes down to you to make the final assessment and judgement of course.....
Note : As always, please note that I strongly encourage you to seek help with whatever is troubling you. With the right help things can improve. There are many sources of help if you look and reach out. Please seek assistance in any and every way possible. You alone must decide upon your actions and take full responsibility for them, and you should always favour seeking help and keeping out of harm's way.