Hi Spook, I've just caught up with this. I am so sorry, your sadness really comes through and I am in tears. I just know I would be exactly the same if my dh did this.
I feel that what he said about not loving you enough to come and look for you speaks more of his definition of love than anything else. If we all gave our love in line with how we were feeling about someone, we would have no loyalty, no forgiving, no relationship would endure, no value in a person could be considered on a day when it was not on display. We would not love another when they had disappointed us, when we were cross, or when we were distracted.
Your dh needs to grow up and learn that love is verb, and a commitment we pledge to someone else when we marry. Not something that can change with the wind. He can give you his love if he wants, but he thinks he has to obey every little whim of his ever-changing feelings.
I think it is likely that he does love you, far more than he realises. When he looked at you and your children and thought you beautiful, it seemed a more rational judgment to me, because possibly at that moment he was weighing up your worth rather than swaying in the breeze.
He has put lots of energy, effort and attention into maintaining his other relationship for a long time, and that is all attention that was rightfully yours. He has failed to put into your relationship what he needed to put in to make it healthy and happy. You may not have even noticed this but I feel that if you look back you will see where he began to drift away and forget the little attentions we all need to keep our relationships sparkling and alive.
If he could be made to understand this then he would realise that giving that attention back to you would revive those fickle feelings of his. He needs to grow up and learn to manage his feelings and use them for the good in his marriage. At the moment he is allowing them to manage him. On this basis he may have many more relationships in his life because he will never truly commit to be with one person even if he wakes up one day and does not have the airy fairy inner feelings fluttering there. It is both partners' job in a marriage to persist through those times and work to get the feelings back. If you have chosen well in the first place, and put in the effort necessary, I believe you can love the same person for life.
I hope with all my heart that he learns this principle, so that he can see how beautiful and valuable you are at all times.