It sounds like his grief is coming from guilt. He was the one left behind. He may have treated her badly and is regretting it. He may not have come to terms with the way he treated her or may be feeling still helpless about never being able to help her. If you try to make him forget her, he will get angry as she was a very important part of his life, albeit a short period. He seems stuck in grief. So how do you fight a ghost? This one is very tricky, but sometimes its important for them to be able to talk about his first wife and why he is stuck, but if you critisize his way of cherishing her death, he will only be angry with you and make horrid remarks. Maybe you can make room for the sharing of him with her, maybe you can't. Often though, when people are stuck, they may choose to be stuck in grief, without realising they are doing it. I understand your frustration of his not showing you love but he may be too scared to. He may have shown his first wife love and she died and he is too scared to repeat it. It is easier to not show vulnerability in emotions sometimes. I know this sounds like a contradiction in terms but if he didn't deal with his emotions at the time of his first wife's death, he won't know how to move on.
He needs help. 20 years is a very very long time. I think you need to reassess your relationship. See if he will accompany you to couples therapy or therapy on his own. If he won't do this, I think it is time to move on with your life and send him packing...he is living in the past and it isn;t fair to you. You deserve more than that,
I read and re-read your post, but I have a bit of confusion. You wrote, "He denies love for me and bases our life on the childrens choices."
So he won't admit he loves you, and that he has only made a life with you because his children made that choice for him?
From what I've read, I think there's a little more going on with your husband than coping with grief from a loss of 20 years ago.
But focusing on the grief part of it, I don't think it's unrealistic of him to cherish memories of his first wife and drive hundreds of miles to visit her grave (unless he's doing this like once a week or some ridiculous amount like that). She *was* his wife, the first woman he'd committed his life to, the first woman he made a part of who he was, and he had very little time to share with her as her husband.
However, if the love he has for her is still so strongly alive for him, rather than just a cherished memory, and it's affecting your marriage negatively, then yes, this is a major problem.
But like I said, I think there's more going on with him than just grieving if he denies loving you and continues his life with you because that's a choice his children are making for him. In that case, then yes, he should seek counceling.