Phaedra was a sore spot for him, and each time he succumbed to her because he had nothing else. He was always running, so he never held onto anything tangible. Few times since had he found someone worthy. Zoe's mother, and now Nike. Someone who quite frankly put up with his smarm, and looked a little deeper than wht history books told.
Theseus died, because he wasn't perfect. Phaedra was a persuasive woman, she always had been. "Phaedra---" and before he could step back she'd locked her lips on his. He didn't reciprocate and immediately pushed her back. "I said no." He wasn't going to go down this rabbit hole again and end up with his tail between his legs.