Am I just anxious or is my husband having an emotional affair?

I’ve been married to my husband for just a few months less than a year. He has an intern at his office who I have always felt uncomfortable with. They text almost every day, including non working days, yet he has increasingly gotten less responsive and invested in similar communications with me. This past weekend when I was out of town, he went to a play with her and other co workers, but she bought his ticket because she “owed him for lunch.” He never told me this. She is frequently at his happy hour events and he will text her after asking if she got home okay. He doesn’t do this anymore with me when I go to or arrive places when he used to. His effort in our relationship has drastically decreased and so has our intimacy. When I’ve asked about why his communication efforts have decreased with me, he will simply say “not everything needs to be replied to.” When I’ve asked about why our intimacy has declined, he says that I’m essentially just so attractive he now randomly feels insecure. That’s really hurtful, feels like absolute BS, and dismissive to me. What concerns me is that he seems sneaky about how much they text, that they get lunch together, and when she is at events during non working hours. Am I being overly anxious? Is there reasonable concern here? How do I even address this??