I'm thinking of possibly encouraging my son to break up with his girlfriend and telling him I have regrets about marrying his mother/my wife
That is no appropriate to tell your son, Why would you do that?
I feel like my marriage was arranged and I feel like I lost the opportunity to find the love of my life
While every parent wants the best for his or her child, it isn't appropriate to project the issues that you have with your relationship with your wife onto your son's relationship. Your son should be able to make his own decisions regarding his romantic life and you shouldn't interfere as a third party. If you have concerns about your son, you should talk with him and discuss potential red flags regarding his relationship that you see and how it relates to your own.
I don't care what you say, I'm going to diminish his relationship with his girlfriend.
That's a horrible thing to do. You should mind your own business and deal with the things in your own life.