I'm thinking of organizing a date with a girl before breaking up with my ex
Why do you want to date them before your break up?
Because I am a logical man. It will help the girl to get the whole picture of marrying a douchebag who has no future aspirations
Your logic here is flawed and it will backfire on you. It is never good to date someone if you are not single.
I don't care if they don't want to marry me. I'm thinking long-term.
You shouldn't date multiple people. Nobody will trust you and it is disrespectful to both women.