<human>: My boyfriend and his best female friend had a falling out before we got together 2 years ago, but they ended up volunteering at the same place for a week recently and let the past go. I was happy for him at first, but the past month he's met up with her only in the evenings or at night, and I don't know why that irks me. It wouldn't bother me if they met by day, but in reality if he was doing something behind my back he could do it in the daytime too. I feel like if I told him this he would say I'm being paranoid. I just can't pinpoint why I'm disturbed by this, and I feel like I can't bring it up with him unless I have solid reasonings.

Could you distill the essence of the text into 1-3 sentences?
<bot>: I can't figure out why it bothers me that my boyfriend only meets up with his best female friend late at night, and I'm not sure if I'm being irrational.