>>>If anyone is bold enough to answer this question, what makes you fall in love
>>
>>Libido.
>>
>>
>>> and what makes you fall out of love?
>>
>>Destrudo.
>
>
>Libido sustains a relationship for three years max IMO. Then it's down to how much you really care for each other.

IOW, do you really care to maintain the libido.

Short of overwhelming physical disability, I don't see a good reason why tenderness should not remain important in a relationship.