My well pump apparently lost its prime tonight, I noticed air coming
out the faucets before it quit entirely. I have a (part) artesian well,
and there is a side pipe/overflow (whatever you want to call it)from
the well that always flows into the swamp out back, all year long. I
shut that off to build pressure into the house so i could deal with the
pump in the AM, but water never came. So I went out, took the fill cap
off the pump and turned to grab a water jug. When I turned back water
was flowing out so I had my prime, I capped it and turned it on and its
working for now.

questions:

What should I look for as a cause of the problem? This never happened
before and I assume it aint a good thing! I did look and listen for
leaks but didnt notice any.

About that overflow pipe-I reopened it but does that need to be open?
Why?

Losing prime in a jet pump could be from air getting into the pump
housing somehow, which means a leak. The first thing to do is check
all the joints for any leakage before you get too far into it, it might
be a simple matter of tightening or replacing a clamp or reinstalling a
threaded connection with some teflon tape.

I think I found the problem in the Air Volume control, which appears to
be leaking (water out, air in).