I’m a 24-year-old woman, and I’m feeling uneasy about my boyfriend, who is 39, having a close relationship with a female coworker.

I'm a 25-year-old woman in a relationship with my boyfriend, who is 39. We've been together for about seven months and currently live in his apartment. He started a customer service job just over a month ago. During his probation period, he worked in an Airbnb office with some colleagues. After passing, he transitioned to work from home, now on the night shift from midnight to 8 AM every day. While working in the office, he frequently texted a female colleague, whom I'll refer to as 'J,' who is also 25. I only learned about her after he mentioned her being nice and supportive when others weren't. They met once during a work gathering, but I wasn't aware of how often they communicated until more recently. He minimized their connection, eventually describing them as 'close.' Noticing that he seemed uneasy whenever he texted her at home, I confronted him about it, as it triggered my trust issues. He insisted he wasn't trying to hide anything and said I could read their conversations whenever I wanted since his WhatsApp was always open on his computer. To satisfy my curiosity, I downloaded their entire chat history. I discovered that they exchanged messages throughout his entire work shift, during his commutes, and even late at night. Their conversations consisted of work-related topics, emotional support, office gossip, and a bit of personal sharing, without overt flirtation. They even discussed having meals together despite being in different places. I chose to keep my feelings to myself and supported him during his work hours, staying up late alongside him. I pointed out that he seemed to avoid texting her in my presence because he feared it might lead to conflict, and although he acknowledged this, his behavior didn’t change much. I noticed that they stopped texting each other goodnight and their communication patterns shifted. We had a small argument recently, and when I didn’t sit beside him until 3 AM, I saw they had exchanged messages since 1 AM. This made me feel that he used that time to reach out to her because I wasn’t there, which raised red flags for me. When I returned, he was replying with very short answers, almost as if trying to downplay their interaction. Now I’m caught in a whirlwind of uncertainty. I wonder if the only reason he toned down their communication was because I was around or if there’s something more going on. I’m also concerned about an upcoming Christmas gathering of colleagues, where he’ll attend with them, and another where I'll be invited. I want to know how to handle their close relationship and if I'm facing a slow breakup. What should I do?