My wife has been gone for nearly 4 years. I have her pictures up and have no intention of taking them down any time soon. I have 3 children who now have, and always will have a close relationship with her, even if only in memory. She comes up in conversations almost daily. If I took down all of her memories it would be like I was trying to wash her from our life. That wouldn't be fair to my kids, her memory, or me.
My father in-law comes from a similar situation, but he has nothing that I've ever seen beyond a couple snapshots of his late wife that he keeps tucked away. His kids seem to have no stories of her, or any real memories at all of her that they've ever shared with me in the 30 odd years that I've known the family. I don't think that my wife's parents, whom I still have a close relationship with as well as their extended family, would like the idea of their grandchildren forgetting their mother. I think that honoring her contribution to our family will always be a part of our life. I wouldn't want it any other way.
On the rare occasion that my father in-law's wife comes up in conversation, which is always very brief, I can see his eyes start to get a bit glossy and red around the edges. To him, it's a subject that still causes grief and sadness that he tries to bury and avoid talking about. By keeping the coversations flowing about my wife and my children's mother, I find that our feelings of loss and sadness are becoming tempered with the happiness of the stories we retain and the joy we had while she was with us, rather than constant sadness that nobody talks about.
I also still have most of her clothes in our closet. These clothes, the university sweatshirt she wore when we started dating, the black dress she wore on formal nights on our honeymoon cruise, the wool sweater that gave such warm hugs on winter days, the "kiss cancer goodbye" shirt she wore to Summerfest when we thought she may survive, and the soft jogging suit she wore to the hospital when she didn't, are the same clothes that I soaked in sobbing tears and muffled screams in the weeks after she passed.
Honestly, sometimes I would like to be able to take them away and let others who need them use them, and I feel that it's becoming time to do that. But each one still holds a memory for me, and for each of our children, that we cherish as we remember a story of where we were with her when she wore a particular item. In time they will go, but I think it will only be after the memories that reside within them become a part of us. It will be a slow process and I think we will do it together.
You may not like having her memories around, but if you try to wash her memories away before he's had all the time he needs to reconcile his life with her, the loss he feels may have a negative impact on your future together. I don't know how long your new love was with his wife before she passed, and 4 years may seem like a long time, but for me it's a fraction of the time I knew my wife, from her days playing 7th grade softball, to 1 month shy of her 40th birthday.
If I was faced right now with a woman who wanted my children's mother, her parent's child, my late wife's memories gone, I would be faced with the inescapable conclusion that she wouldn't be a good fit in our family.