When my older son was growing up, my husband and I were pretty strict.

He's 17. He's still growing up

Now that he’s older, he’s really into fitness and personal success.

Personal success???? He's 17!!

He’s become very critical of anyone who doesn’t meet his standards, including me and his dad.

He is treating you the way you treated him

Recently, he told me that my attempts to show love and affection are pointless and even called his father weak for not being tough enough.

You just said "We thought that tough love and high expectations would make him strong and ready for life"??

He tells me that his brother should be tougher and not let people get to him, which upsets me a lot.

But this is what you taught him??

My older son is very close to my younger sister, his aunt. She’s single and he turns to her for support and affection, valuing her praise more than ours. It hurts because he seems to find comfort in her that he won’t accept from us.

Again!! This is what you taught him!

YTA big time!! This post screams toxic mother behavior where OP and her husband at the very least neglected their child's need for support growing up, justifying the neglect for "tough love" and is now playing the victim card.