First of all, make sure you do all your own research, just take what we say as 'advice' and nothing else.
Secondly, before you buy anything, go to your local range and rent a variety of 1911's, Kimber, Colt, whatever you see---and shoot some other .45's (HK, SM M&P) as well, so you have a good frame of reference. The $$ you spend on rental fees is well spent, and hey--it's an afternoon at the range, what's more fun than that?
Finally, remember for home defense, ammo is crucial as well. Make sure you research the various loads out there--range ammo, and 'tactical'. There are a lot of excellent personal defense rounds being produced right now.
If I were in your shoes, I'd probably grab a nice, used Kimber, full size, and load it with Hornady Critical Defense. For range ammo, Blazer Brass is cheap and decent.
Good luck. Make sure you include your girlfriend in your range trips!