Don't mind me

I'm sure I'm not your priority
I'm more of an accident
The product of that "incident"
Now you have a much more stable life
Happy husband
Happy wife
Two more added
Within the sacred ring of matrimony
Obviously I was outside of that ring
My the existence depended on a fling
I'm more of an inconvenience
A reminder of the ugly truth
The remnant of that darn booth
I didn't quite get the memo
From casual to formal
I'm not sure what role I should play
Of course I'm nothing like her
I'm so far from him
I'm a disgraceful character
A disappointment at the seam
Happy family
Happy life
But I was born when you were not his wife
That changes everything
She came when you were hitched
I feel my birth was bewitched
Just my opinion
Don't kill me now
Don't call me a manipulative cow
Semantics you say?
Well the devil is in the details
I blame your radical behavior
For all the he times my coin fell on tails
I sound heartless don't I?
I just wish I had her chance
I just wish I could have a glance
At the life I would've had
Had you gotten me
When you were a little more mature
You're parenting would've been less unsure
Help me understand
How your failing marriage is all my fault?
How I'm the rot that made your wood wilt
Yes you love me
Sure no doubt
But love isn't all that it's about
You can't change my insecurity
My constant feeling of inferiority
To him
To her
Those born within the marital rings
My very mature, better than me
Siblings.