What Breathesgirl said.
Also you wife may be having some New Relationship Energy (NRE) which puts a glow around their new love. When your love is in NRE, it is easy to feel insecure in general.
There is NOTHING juvenile in your feelings. You feel what you feel. The only thing you can control is how you behave. One thing you might try doing is spend more time with the boy friend. As you get to know him, he becomes more human and less a djinni of terrible prowess and wonder.
You may also want to look thru some back posts here on insecurities.
Good luck! Warm regards, Rick.