Most investors understand that wealth compounds over time. What fewer people appreciate is that friendship does, too, and the return on that investment may be just as consequential for a fulfilling retirement.As a wealth manager and retirement researcher, I spend a great deal of time analyzing what separates the happiest retirees from those who struggle. The answer isn’t always a bigger portfolio. It often comes down to community. The data are clear, the anecdotal evidence from retirees I’ve studied is consistent, and yet this remains one of the most overlooked dimensions of retirement planning.Here is what the research actually says,…