[Idiom] "A bit on the side"

[Elena22]

"
[GIRL (Grabbing a letter from Fantine)]
And what have we here, little innocent sister?
Come on Fantine, let's have all the news!

[Reading the letter]

Ooh..."Dear Fantine you must send us more money...
Your child needs a doctor...
There's no time to lose..."

[FANTINE]
Give that letter to me
It is none of your business
With a husband at home
And a bit on the side!
Is there anyone here
Who can swear before God
She has nothing to fear?
She has nothing to hide?

source: Lyrics On Demand - Song Lyrics, Lyrics of Songs, Free Lyrics, Free Song Lyrics, Rap Lyrics, Country Lyrics, Hip Hop Lyrics, Rock Lyrics, Country Music Lyrics, Music Lyrics"

Above is a part of the lyrics of a song "At the end of the day"
from the musical "Les Miserables".

Fantine is a major and an important character and
the situation here is that Fantine's co-workers
are jealous of Fantine's beauty, that she gets most attention
from foreman in the factory.
Fantine and the woman who snatches letter from Fantine
are all workers working in the factory.
She says "It is none of your business. With a husband at home
and a bit on the side!"
I don't understand what that means... Is it an idiom?
Help me please?

 

[bhaisahab]

"
[GIRL (Grabbing a letter from Fantine)]
And what have we here, little innocent sister?
Come on Fantine, let's have all the news!

[Reading the letter]

Ooh..."Dear Fantine you must send us more money...
Your child needs a doctor...
There's no time to lose..."

[FANTINE]
Give that letter to me
It is none of your business
With a husband at home
And a bit on the side!
Is there anyone here
Who can swear before God
She has nothing to fear?
She has nothing to hide?

source: Lyrics On Demand - Song Lyrics, Lyrics of Songs, Free Lyrics, Free Song Lyrics, Rap Lyrics, Country Lyrics, Hip Hop Lyrics, Rock Lyrics, Country Music Lyrics, Music Lyrics"

Above is a part of the lyrics of a song "At the end of the day"
from the musical "Les Miserables".

Fantine is a major and an important character and
the situation here is that Fantine's co-workers
are jealous of Fantine's beauty, that she gets most attention
from foreman in the factory.
Fantine and the woman who snatches letter from Fantine
are all workers working in the factory.
She says "It is none of your business. With a husband at home
and a bit on the side!"
I don't understand what that means... Is it an idiom?
Help me please?

In that context "a bit on the side" means an extra-marital lover.

 

[emsr2d2]

"A bit on the side" is someone you are having a (secret) relationship with. Normally, it means you already have a husband/wife/boyfriend/girlfriend who is considered to be your "official" partner, but you might be messing around with someone else in secret. It's basically the same as "having an affair".

I'm not sure what is happening with the formatting of your posts. Look at where the breaks are in your paragraphs. Are you writing your posts in another program and then cutting and pasting them into UsingEnglish?

 

[Elena22]

I copied pasted the lyrics from the website. See the source mentioned above? It's that.

 

[emsr2d2]

I​can see how it happened with the song lyrics but the rest of your post has strange formatting too. The words should stretch all the way across the text box like they do in my posts.