I'm a Mississippi gal, and my Mama made Hoppin John and collards every New Year. I always loved the peas and rice, but have never been able to abide collards. WAY too bitter for me!
Mom said the first frost 'takes out the bitterness' but, I couldn't tell the difference.
You might be overcooking them.
Try sauteing a little onion and red pepper in bacon fat. Add the stemmed and cleaned collards, some chicken broth and a little sugar.
If you have ham hocks, you can add, maybe 2 of them now. Simmer for about 2 to 2-1/2 hours.
They should be excellent.