My suggestion is if you don’t feel it and he responds back, you need to respond in return.
Words don’t matter, actions do, so why do you love me?
Thank you the kindness, but I don’t love you.
Why do you think I don’t respond to I love you anymore? You need to learn to read the room better.
Or tell him stop saying it since it is meaningless without action. But then you may need to tell him how he has to act without the knowledge of success.
What I have found recently through some work is this in a poor persons analogy. Think of the act of the act of saying I love you as an act of a quickie in sex. This is fine and good sometimes, but in reality if used all the time sucks.
Making your partner have less stress, freedom, sex the way they want, and happy moments is the foreplay that is necessary to make one want to have it.
If he is dense you can always say after he says it, well I don’t so please stop projecting your insecurities on me.
If you love me, then agree to an open marriage and the nesting thing you asked for.
Be well and be strong.