TIFU by walking into my friend's room

So today I was in my hostel. Two rooms share the same connected balcony, and my good friend lives in the other room. We usually hang out together, and he sometimes comes into my room, mostly to smoke.
He had also left his lotion and flashlight (he is active like daily jerking and horny I say most of the day) in my room because he wanted to keep them hidden from his roommate, so he came over earlier to get them.
Today, I was in the washroom when he called me, but my phone was in my room, so I didn't hear it. About five minutes later, I came out and went to the balcony to see what he wanted.
His door was slightly open, just a few centimetres, so I walked in without knocking. And then I suddenly saw him lying on his bed, aggressive masturbating
I literally froze for a few seconds like, “What the fuck did I just see?”
As soon as I realized what was happening, I quietly closed the door and left. He noticed that I had seen him, and I immediately went back to my room, completely shocked and awkward.
Looking back, I probably should've knocked first but knocking is generally not used if it is locked u knock otherwise just go in, but the door was already slightly open and I genuinely thought he brought cig to smoke
I'm dying of embarrassment
So today I was in my hostel. Two rooms share the same connected balcony, and my good friend lives in the other room. We usually hang out together, and he sometimes comes into my room, mostly to smoke.
He had also left his lotion and flashlight in my room because he wanted to keep them hidden from his roommate, so he came over to get them.
Today, I was in the washroom when he called me, but my phone was in my room, so I didn't hear it. About five minutes later, I came out and went to the balcony to see what he wanted.
His door was slightly open, just a few centimetres, so I walked in without knocking. And then I suddenly saw him lying on his bed, aggressive masturbating.
I literally froze for a few seconds like, “What the fuck did I just see?” Whyyyy
As soon as I realized what was happening, I quietly closed the door and left. He noticed that I had seen him, and I immediately went back to my room, completely shocked and awkward.
Looking back, I probably should've knocked first, but knocking isn't really a thing between us when the door isn't locked. We usually just walk in. The door was already slightly open, and I genuinely thought he come to chill or hang out or brought cigarettes to smoke.
The actual fuck-up was me assuming it was safe to just walk in like I normally do.
Now whenever we see each other, there's this weird unspoken moment where neither of us knows whether to acknowledge what happened. I'm honestly dying of embarrassment.
Bro got caught in 4K
TL;DR: Went to my friend's room because he had called me, walked in through his slightly open door without knocking, and accidentally walked in on him masturbating. He noticed I saw him, I immediately left, and now we're both pretending nothing happened.
Taken little help to write but sequence it is