My best friend’s relationship

So for context, me (20F) and my male friend (20M) have been best friends since middle school. We have one of those friendships that, from day one, endured the highs and lows of life. At this point, we think of each other as siblings. We have been going to different universities since the past two years but are still closer than ever.

Since the past year, my friend has been head over heels for a girl at his university after going through such a dark time with his last relationship. I couldn’t be more happier that he has felt safe to open his heart again. However, I learned that the girl also has major trauma from her last relationship. Her ex cheated on her with his own female “friend” throughout their entire 5 year relationship. My heart absolutely broke for her when I found out and I immediately recognized how my friend’s and I’s dynamic was going to possibly be triggering for her. The first time me and her got to talk privately, I tried to reassure her that she had every right to be cautious and that she can talk with me privately if she ever feels the need to establish a boundary.

Since their relationship, my friend’s and I’s dynamic has obviously changed quite a bit. I always extend the girlfriend an invitation to our hangouts and am more self-conscious of how I interact with my friend, even when it’s just us two. Meanwhile, I know my friend has done everything he can to make her feel secured and loved in their relationship. When he talks about her to me, I can just see that he loves her so much. And he is the type to express his affection in every way possible.

There was nothing that made me feel that there were any issues until last week, my friend broke down over the phone to me. He told me that his girlfriend has been struggling with accepting our friendship, but he was also terrified that we were drifting apart. I am truly at a lost on how I should approach this considering I thought that I was doing everything I can to respect their relationship while also not losing my best friend. I feel so torn between helping him, but also being afraid that I will only make the situation worse. Part of me also feels that ultimately, the girlfriend is acting out of immense trauma from her past relationship. And that is something completely out of my hands and partially, out of my friend’s hands too.

Has anyone dealt with a similar situation?