"Faking it" burns up a LOT of mental (and physical) energy for someone with our neurological configuration. The truth is we simply aren't equipped for it and though we can manage to paste on a fake smile and walk our way through it for brief periods of time, at the end of that act, we are DRAINED and require solitude and quiet personal down time to recuperate and recharge. For me, the recovery time takes at least as long (and usually twice as long) as the social performance did in the first place.
I think of it like this: When it comes to the brain's ability to interpret incoming sensory stimuli, including sound, light, voices, music, facial expressions, body language, etc, etc, we were shipped out with slightly substandard social processing chips. Our brains can process the data, but its being shoved through a smaller funnel than a normal brain's social filter has, so we're always a bit behind, and trying to play mental catch-up, so some details get missed, forcing us to fill in the gaps with guesswork - and its very exhausting.
Which is to say, by the end of the work day, you just don't have the mental energy left to keep listening and processing and reacting appropriately. You should probably explain to her that this is a common problem for Autistic people.
If you can't find a job that allows for more solitary working conditions, then you may need to set aside part of your weekend, just to do things with your partner. If you have a two day weekend, spend one just relaxing, or doing whatever needs to be done to maintain the household and set the other aside for things you enjoy doing together.