Hello Lee, ]
Sorry for your loss and well done on taking this first step to travel again. Many of the people you'll travel with will be in a similar boat having lost a loved one, some recent and some maybe many years ago and they will all have felt the same at some point. They will understand if you're sad, they will be friendly but won't push you to join in if you'd rather be left alone at times.
Of course you'll miss your wife and at times be sad that she's not there to share it but you'll also have a good time and learn to realise that it's ok to do that. I found that giving myself permission to enjoy life after my husband died at a relatively young age was hard. Taking my first solo trip helped with my healing, obviously I still miss my husband and wish for the oid days, but I can honestly say that solo travel has enhanced my life.
Alhough you're part of a group you can mix in or go it alone as much as you like. Tell people as much or as little about yourslef as you wish. There's no compunction to join in if you want time alone but there's always someone around if you want company.
It's not an easy decision to travel solo but I'd encourage you to find somewhere you'd like to visit and just book it, there's nothing to lose but, I've found, a lot to gain.
Best wishes and happy travels
Rose