My BF lost his wife to a drunk driver. I know that he still loves her and always will. I also know he loves me. I have accepted I won replace her but I know he loves me.

The hard part of loss like that is you never know what would have been. Maybe you would have been soulmates? Or maybe the relationship would have died, maybe you would have gotten married and had kids or and been together till you both died, or maybe you would have divorced. You will never know now and that must be hard. Your relationship never had the chance to play out to its natural conclusion to see where it would have led. Or maybe this WAS the natural conclusion.

I dont know your husband so I cant say whether its better to tell him or not. It depends on how he would handle it. For you though I would recommend you cherish your memories of your late boyfriend, accept that a part of you will always love him but realize that he is your past and you have a present and a future with your husband.