traveling to US - I have a valid ESTA linked to my passport from a year and a half ago. About to travel in a months time again. When reading about the requirements for re-application, I saw that change of civil status is one of the requirements. Back in the day I lived with my partner - now we split and I live alone - so I decided it would be safer to re-apply (no changes in name). However Later I realized there is not even a field for civil status in the application, so now I have 2 valid ESTAs linked to one passport. Would this be a problem?
Your first ESTA is probably no longer valid. You can check at https://esta.cbp.dhs.gov.
See for example When my ESTA expires how do I renew my application?
You do not need to wait until your ESTA expires to re-apply. You may do so at any time before, on or after the expiration date of your existing ESTA. Should you receive the message "A valid, approved application with more than 30 days remaining has been found for this passport. Submitting this application will require payment for this application and will then cancel the existing application." you will simply continue with the application to begin your new application. Your prior ESTA will be cancelled and replaced with your new application.
Even if your first ESTA was not cancelled because of some error in the system, it isn't your fault, and you should expect no problems to result from it.