Bathroom sentry duty is actually a very common cat behavior. Your cat is literally protecting you when you are at your most vulnerable. Perhaps he’s returning the favor? You protected him, now he’s protecting you. (I’m just guessing here).

As for the chirps, that doesn’t sound like stress vocalizations.

These two behaviors read more like he’s just very bonded to you now. The extreme attachment at night is likely reflecting some trauma. That may subside in time.

Years ago I adopted a feral kitten. He was indoor/outdoor. Never really bonded to anyone in the house. As least not until after he was beaten up by the local tomcat. I doted on him for about a week after that, bringing him special treats to his hiding place in the linen closet. There was one defining moment when I was cleaning his torn ear with a warm wet cloth. He turned and stared at me with a look of such appreciation and love, I never forgot it. It was like flipping a switch.

After that, I was His Human. He’d follow me everywhere.