If he is not telling her about you, then I can see trouble brewing. It may be you are keying into the problems his relationship with her can bring. Part of jealousy is fear of loss. So maybe you are worried this will hurt your relationship with him.
It is very hard for someone in NRE to see the crazy flaws of someone you are with. It may be a lesson he has to learn, but hopefully not something that will damage your relationship with him.