I think the answer is to be completely self-contained. Learn how to be comfortable going solo, and figure out how to show your wife that it can be safe. Many people on this site wouldn't think twice about solo hiking and backpacking in summer, learn from them what works.
Once you are capable and willing to go on your own, friends and hiking partners become added bonuses, not requirements. If your friend (and he is your friend, don't be too hard on him) backs out it won't be a big blow. Your weekend won't be ruined and your friendship won't be strained.
Accept that people won't always want to do what you want. These days I will often decide to change plans or cancel if the weather turns nasty. I just don't enjoy it very much. Have a backup plan if you don't feel comfortable with the original plan now that it's solo. But if you want to avoid being disappointed you need to remove other people from the cirtical path. So you can get out on the non-critical path.
-dave-