If it is a rare thing for you to go out, he should not be complaining. It does seem a bit weird that you would want to go out with the same new coworker twice in one week, but you certainly have the right to.
Not the OP but why is it weird to spend two evenings out with the same person? It has nothing to do with that. Your answer is passive-aggressive. First you say he shouldn't be complaining abd then you say it's weird to go out with same person twice. Why is that weird?
Honestly, I would be annoyed if my husband was going out with the same friend two night in a week, absent some special event like the friend's birthday or a concert, and I was alone watching our kids two nights for that reason. I want DH to stay in touch with his friends and maintain friendships, but seeing someone two nights in one week isn't necessary to do that, and I'd likely consider DH to be focusing on the relationship with that friend to the detriment of his responsibilities to our family. If he had two different friends that he wanted to catch up with, and they were both only available in a given week, I'd feel differently. Doesn't seem that complicated.