Is it..
Camp
I'm usually short-lived but my fire burns bright, a site for sore eyes
Temporary accommodation, campfires burn bright.. a campsite for rest
A thing for the adventurous or the obsessed, sometimes followers,
Adventure camp, or camping in general, not sure about obsessed (retreats or rehab?)
There are a lot of us in the army, but they give us the boot,
Bootcamps and there is a lot of camping in the army
Those that don't like me might give me a bigger head, give me a break!
Not sure about this one.. yet!
OP explanations
I'm usually short-lived
Most camps are temporary
but my fire burns bright,
Campfire
a site for sore eyes,
Wordplay! :)
A thing for the adventurous
Some camp out in the wilderness and the likes,
or the obsessed,
Others camp out in front of stores etc. ...
sometimes followers,
As in a "Camp Follower"
There are a lot of us in the army,
Military encampments
but they give us the boot,
Boot Camp
Those that don't like me might give me a bigger head,
Glamping...
give me a break!
"Break camp"