Just tell him you love him and will always be there for him.
limit the amount of memorabilia visiable, keep it all in a special place, and let the kids know where that special place is, but keep it out of sight.
honestly he seems depressed,
understandably of course.
He needs to be kept active, in sports and activities,
ask him what he misses the most about his mom,
what special things she would do for him,
and try and do them aswell.
there is no real way to deal with this, only time will heal
he is a child who misses his mom, there isn't much you can do about it.
I suggest try filling his mind with other thoughts.
try and remember that when you say how wonderful your babies are, he misses his mom saying that to him,
share special memories of him as a child if you can.
When you were a baby stories---- , MAke stuff up if you have to and that will definatly make him feel better.
I know my son misses his father, I am remarried and live in a diffrent state.
I tell my son" When he was a baby stories", and it makes him feel better,
He usually misses his dad when I am paying particular attention to my new little guys. and feeling jealous,
So I try including him in those statements,
like I have the 3 best children in the world, I tell my oldest he is special to me, more special than his brothers.
because he and i knew eachother for 10 years before his brothers came,we've been thru alot together.
I also include him by asking him to help with the kids and then praise him often.
He knows I love them all equally but diffrently,
as you do with All children,
but it lets him know he holds a special place in my heart that his brothers don't fill.knowing that comforts him.
Good luck and I hope this helps
M