I was the "bad" parent even though we never separated. My AH wanted to be cool and liked and he could not say "no". It was always "go see what your mom says" or "I'll ask your mom" or "don't tell your mom". It was so frustrating, and aggravating to always be the one to "ruin their plans" and have to receive the full teenage tempest of emotions.
Now that my kids are adults (mid-twenties), they have come to appreciate the boundries that were placed for their own good and out of love. They appreciate that I was basically a "single" parent when it came to actually parenting. That's not why I did it, but it is nice to get some acknowledgement and gratitude after all that teenage angst. It is gratifying to know that being strong and consistent has paid off in having well-rounded mature young women in the end.
Stick to your guns. It's tough and oh so lonely, but it is worth it, every single door slam, every single stomp off, every glare, all of it!