Whatever you decide to do, don’t listen to this guy.Be a man and put your foot down, I am gonna marry this second wife if you want a divorce go ahead or if you wanna stay I am gonna marry her regardless. She will cave in and decide to let it go lest she become divorcee the worst fear of many ladies.
If you want to get a second wife. Do so in an honourable manner without hurting the mother of your children. If you have the financial means and you are able to fulfil the responsibilities that come with it then go ahead. Speak to her and try to get her on board.
Marrying more than one is not a privilege, but a huge responsibility which you will be questioned about.