When my kids were little the only "me" time I got was in the middle of the night once the hubby and kids were in bed. I would run errands, like going to the grocery store, at 1:30 am sometimes. It wasn't a good place to be. I was nothing but a wife and mother, and in my opinion that's not healthy.
As my kids got older (and I got more and more burnt out) I HAD to take more me being me and doing things *I* enjoyed (not just errands for alone time ... that's NOT something I enjoyed).
Now that my kids are almost grown and out of the house ... I come and go almost as much as I please. I have a LOT more me time to do the things I really love doing. And I have some friends I get together with on a semi-regular basis ... we all try to get together every couple of months depending on schedules.
As a compromise ... if your friends are doing "girls night out" every Friday why don't you join them once a month (give or take)? You still get plenty of hubby time and still get some real personal time. That's what I would do anyway :)