hard to say from what you have written, and i'm projecting alot, But if i were in your shoes Yes i would be jealous that your husband would rather spend time with this guys than you.
I'm hearing loud and clear that people are telling you that everyone needs some friends outside the marriage.
I can sort of see that they could get sick of mcdonalds, but do they realy have time at lunch for a sit down resturant?
Is there no one else at work for hubby to go out to lunch with??
I think that was my sticking point, that it was just ONE guy all the time, but if he only works with a few people or he is management and most aren't then maybe i could understand it better. if there are tons of people he could be inviting but is only picking one, or if he is shunning others in the breakroom to be with this one guy then that would be weird.
I would worry if from what you hear if they are emotionally close or just talking sports over a club sandwich..
As for him not introducing you, just stick out your hand and say hello I"m so and so and wait for them to give you their name. Then you'll know who these people are.