Added a Domestic Partner as a Dependent, are my tax implications this much moving forward?

I recently added a dependent (Domestic Partner) 2 weeks ago and received my first paystub with this change. There is also a 3.5% raise included but that should be negligible. I'm trying to determine what my tax implications are going forward.

I understand that I am now taxed on the amount the employer is paying toward the premium for my domestic partner but am a little shocked at the increase (~$600/2 weeks) and just want to make sense of it and try to narrow down the difference between Myself and Myself + Dependent. Close to a $600 reduction per paycheck was not what I had calculated unless the Retro Taxable Benefits is causing this difference for only this paycheck.

For the Taxable Non-Cash Events, are the Retro Taxable Benefits calculated as if the dependent was carried since the first of the year and i'm paying taxes on those amounts?
Also, this is the current imputed income as stated in my benefits: "The amount your employer pays towards coverage, $456.61/pay period, will be added as Imputed Income to your Form W-2 as taxable income"

I also did receive a bonus of $2532.63 between my pre-dependant paycheck and Post Dependant paycheck. I am wondering if that is the Retro Taxable Benefits that could have been applied to my latest paycheck.

I've included a screenshot of a paystub before the Dependent was added and the latest one.

Thank you for any help you can provide!

Pre-dependent Paystub

Post-dependent Paystub

submitted by /u/Wide_Shift4797
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