My boyfriend still feels bad about something that happened long ago?

So I was with my boyfriend last night and here’s a little backstory:

in the summer, we ended up working in the same place and making a ton of new friends. He made lots of friends with girls and particularly this one girl. This one girl invited him to an after party that was going on after a different big get together the workplace was having.

so at 1:00 am they went to her property with a little cabin and a few beds. Not enough beds for everyone so my boyfriend slept under the stars right by the fire. This particular girl, worms her way under his blankets and complains that she is cold. He then put his arm around her and they apparently talked about how nice it is to just be friends and cuddling.

He was terrified i would break up with him, and I admit I was hurt by it but he was really sad and said it meant nothing, that they were just cold, and he made it up to me by taking me for dinner and even the next party we went to he was super affectionate and was stuck to me all night. He proved he was sorry. He felt really bad and like he disrespected us but I forgot all about it until now.

Then last night when I was with him, he tells me he saw something similar on TV and that it reminded him of what happened and that he still feels really bad. But I told him it’s all okay and that we are past that, to which he thanked me with a kiss and an “I love you so much”

why does he still feel so bad about it after all this time? Makes me think something more extreme happened than cuddling even tho he made sure to tell me NOTHING HAPPENED.
My boyfriend still feels bad about something that happened long ago?
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