How serious is my oil leak? What could be the cause?

Just bought a used farm truck out of
desperation. It's in rough shape from
an aesthetic standpoint but
otherwise it's been well maintained.
My friend borrowed my car where it
sat outside for a few hours in 0
degree windy weather. He had
trouble starting the car. I'm guessing
it's an older battery so that plus the
cold and the fact that he had multiple
assessories (heat cranked, radio,
lights ect) turned on is what I'm
guessing the cuprit is. It's hesitated
to start a few times but never not
started but it's only every happened
in below freezing conditions though it
wasn't as cold as the night that I'm
referring to. Will be getting new
battery with high cold cranking
amps.
The problem is that when he couldn't
get it to start he tried over and over
repeatedly without pausing or turning
off the acessories...all while
stomping on the gas. A jump ended
up getting it to start. When he finally
brought my truck back he said as
soon as he parked it white smoke
came from under the hood. He said
as he was parking it made a funny
"whirring" noise and he said it
smelled of rubber.
Upon further inspection and
checking all of the fluids this what I
have found:
The engine compartment has engine
oil everywhere, mostly on the drivers
side. It's on the fan, belts, drivers
side of the radiator and all over the
bottom of the truck. But most of all in
the drivers side wheel well. Like all
over the wheel well and axel.
The car is actively leaking engine oil
and only engine oil even when at
rest. Overnight I'd say it left 6" in
diameter puddle on the drivers side. I
don't know much about cars so I
can't identify where it appears to be
coming from.
My oil level is low. I'd say at least a
quart is missing.
My transmission fluid is low though I
haven't checked it before.
No other fluids are leaking or in the
engine compartment and all fluids
are of normal color. Also the oil leak
on the right side is the only spot.
The oil was changed about 6 months
ago & has been maintained regularly
though it does need only.
Nothing else seems out of place.
When I purchased the truck I noticed
a tiny bit of oil stains, not residue and
certainly not fresh...in the drivers side
wheel well and only there. Don't
know if it had any relevance or is a
reoccurring problem, just figured
someone spilled.
Any advice would be much
appreciated. I need my truck but I
unfortunately don't have money to fix
it right now. So ether it sits until I
have money to get it looked at and
fixed or hopefully I can just keep an
eye on the oil level and drive it short
distances until I have the money to
fix it. I'm just afraid that given how
much oil it lost in a short period of
time that it may happen again only
far worse and I can cause some
serious engine damage.
Thanks for taking the time to read
this!

P.S. It has about 142k miles on it if
that's of any potential relevance. I
don't know much about it's history of
repairs.