I've had numerous car buddies over the years. Many of them moved on to less expensive hobbies or gave up cars altogether. I still have one friend that I call with questions and vice versa, but due to getting older, married and kids, we no longer have a whole lot of time to hang out and just wrench. His free time is spent being a dad to a 2 year old, and if have any time to myself I go mountain biking with my bike friends instead of working on the Z.
The Z, for now, has taken a back seat to work, married life and bikes. If and when I do get the motivation to finish it I'll call up my friend and ask him if he wants some free beer and invite him over. For now, my friend's and my Zs are sitting under tarps in our respective backyards waiting for us to adjust our priorities.