There is literally nothing you can do that won’t make you look like a crazy, jealous and stalky ex girlfriend.
If you are unfortunate, he might end up marrying the girl and you will never get to talk to him again. I don’t want to sugarcoat it but if a guy lets a girl decide whom he talks to, then he is pretty serious about her. He might not even be able to cope with your silence and start acting a little crazy (angry texts, angry phone calls, mean facebook messages). This means that the only reason he was so calm about the breakup is because you were making him feel like he still has you.
This means he still hasn’t dealt with the thought of losing you forever.
Like I say constantly through this site, the no contact rule is for you.
It’s for you to decide what you want in life and what is good for you.
If he doesn’t respond, then he is still doing no contact.