Is my fiancée (31F) cheating on me (33M)?

I got into relationship with a 31F through a friend circle about 1.5 years ago (in mid 2023). I started living in with her in her 3 bhk apartment shared with 2 other female flatmates. She said she was having feelings for me. Since, the apartment had three occupants multiple of their friends visited the apartment. Obviously, a few of other flatmates’ friends became my GF’s friend. One of them was a guy whom she called ‘bhai’. Although, they had met barely an year ago, they both had very brotherly feelings for each other as per my GF.

One day, I entered my GF’s room to find that the ‘bhai’ guy was laying on her lap and she was stroking his hair. As soon as both of them saw me, they got shocked and the guy got up and went of the room as if feeling guilty.

I didn’t see them in such a position for next one year, until the Diwali party at another friend’s house in which I and my fiancée, as well as the ‘bhai’ guy was invited. I had long forgotten the first episode (although it shocked me) because I gave her the benefit of doubt, mostly, because she called him ‘bhai’. But, in this year’s Diwali party I entered one of the rooms and found that, the guy was taking a mirror selfie with my fiancée hugging her tightly. They were lonely in the room. As soon i saw they, they again separated as if in shock and guilt.

After getting back home, I confronted my fiancée regarding this behaviour and said that I wanted to breakup. On this she begged and cried in front of me that she loved me a lot and they (she and ‘bhai’) have kind of ‘brotherly’ vibe with each other. However, i was not fully convinced, but she cried and broke down so much in front of me, and said that she loved me so much and would never do this to me - that ultimately I gave up and didn’t breakup.

Now, today i was checking my fiancé’s Instagram and i found a comment in it from 2022 (when they had newly met -within 1 year or so) , in which the group which included her and that ‘bhai’ guy had gone to Goa. And in her whole Instagram page i only found one comment from him and a reply by her, which has made me even more suspicious. I have attached the Screenshot of the comment section of that post. I can’t post the pic obviously- but, it had 5 people, my GF and ‘bhai’ guy also. My GF was wearing shades and he seems to be complimenting her looks. I don’t understand her reply TBH, if she is stroking her own ego by calling herself a hottie or she is calling the guy hottie who she recently had ‘intimate relationship’ in the trip.

What do you guys think about this dynamics? Is my fiancée cheating on me, or am I having a confirmation bias?