My (21M) GF (23F) strange relationship with guy. Is this normal?

LDR. met her two years ago, in person (of course).

She knew this guy in February and says he’s her best friend in the country she’s currently studying.

Now, the weird thing: she told me the last time we saw each other -10 days ago- that she had stayed in this friend’s house the previous week, when precisely she was super distant and just called me for two minutes at nights. She confessed she wanted to tell me in person, that he’s just a very good friend; that she stayed in his house cs she felt sad and alone.

I don’t like this, but I love her. We discussed over this issue in person, but every time she mentions him, it’s like a stab on my heart.

Oh, I forgot to mention that in the end, he invited both of us to have dinner, but tbh I didn’t quite like the idea because it would ve been with his parents and being this guy, I hadn’t liked to be there.

Even so, it’s still super weird. She has a folder on Instagram with a heart as a cover with just pictures of us of both of us and surprise... two pctures with him wtf

TLDR: sus gf’s relationship with a guy friend. I don’t know if it’s normal to feel like this and what to do.