My second try, based on the comments below:
Morse code
This is the fourth of the series,
are you becoming tired now?
One of my long-time friends carries
what you can put to use somehow.
"Long-time" contains a dash, part of Morse code
Not in every occasion though,
in fact right now he isn't here...
Three dots but no dashes here
But if you wait for some time though,
he might decide to visit here.
Dash indicates a pause in a sentence
He's very short for your standards,
and right now he is only two.
Just two small parts, really small parts,
they're quick to make, and little too.
Two parts of Morse code: dots and dashes
Usually you cannot see him,
unless you look into the past
of those ones who utilize him
or make their current state the past.
Morse code is not used in recent times.
I can't tell you're confused or not,
but tell you the question I can.
Whether you have found it or not,
can you tell me, who is my friend?
My first try which was wrong:
I think the answer is:
Comma
This is the fourth of the series,
are you becoming tired now?
One of my long-time friends carries
what you can put to use somehow.
Long-time friend = comrade, contains the letters of comma
Not in every occasion though,
in fact right now he isn't here...
Notice this line doesn't end in a comma
But if you wait for some time though,
he might decide to visit here.
Commas indicate a pause in a sentence
He's very short for your standards,
and right now he is only two.
Just two small parts, really small parts,
they're quick to make, and little too.
The round dot and the tail
Usually you cannot see him,
unless you look into the past
of those ones who utilize him
or make their current state the past.
Usually commas are not at the end of a sentence, so you have to look back for it. I think "those who utilize him" means "sentences" and "those who make their current state the past" means "periods".
I can't tell you're confused or not,
but tell you the question I can.
Whether you have found it or not,
can you tell me, who is my friend?