It reminds me of something which may or may not apply, but seems semi-related. I remember reading about attachment theory; the model/framework of understanding attachment, where some developed healthy, secure attachment and some developed maladaptive forms like anxious attachment, avoidant, etc. And there is this idea that someone who is used to the high highs and low lows of a maladaptive form of attachment can find it almost boring when they encounter secure attachment. Perhaps that's something like what you're going through. Worth bringing up with your therapist though.