Dual citizenship is perfectly legal under US law. I am a Naturalized US citizen but also a citizen of 2 other countries. This is perfectly legal and the US government is aware of this. It would also probably surprise you that I legally have 3 passports. Check the State Department’s website on this issue.
When I acquired US citizenship, I was not required to give up other citizenships- the oath I took only required me to swear off any other allegiances.