Several things:
-First, how long have you been with this girl?
-Second, what is your track record of character judgement of your significant others?
-Third, why bother with a can on your home defense firearm?
Odds of needing to use a home defense firearm are very small, and doing so once... or even several times, isn't going to make you deaf. You're likely to experience auditory exclusion in the event you do have to use it, so you won't notice the noise anyway. And finally, worst comes to worst and you for some reason get felony charges (say, voluntary manslaughter) for your self defense... doing so with a silencer tacks on a mandatory 30 years. So that takes what would have been maybe 2 years prison for shooting dead two people who broke into your home, one of which took two rounds in the back, on the front porch, and turns it into 32 years.
Now, lets throw another "what if" your way. This GF has a friend stop by. Said friend has a closet gambling addiction and raids your bedroom for items of value while GF is using the bathroom. Your silenced pistol shows up at a murder that evening... You think you'll be able to get off by just saying "it was stolen by a visitor when I wasn't home"? Not likely since you illegally left it in constructive possession with your GF.
Sure, none of this is all that likely to happen. But how likely is it that a silencer is going to make the difference between you living through a break-in, or dying during it?