I don’t even know…just venting

My BF of over 4 years came up to me while I was doing dishes and had a bullet mark on his forehead handling me a handful on them telling me to hide them from him. He then goes into he couldn’t make the gun work and that he just tried pushing the bullet into his head. I was panicking and called his best friend over to talk and calm him down along with me and then he just starts yelling at me telling me why did I bring his friend into this and I simply just didn’t know what to do or how to comfort fully within this situation. He then just starts getting pissy and trying to pick a fight literally over it. Later he left for a few days before coming back and I found out the same night he left he went to go mess around with some other females and the friends I called over to help was in on it. When I confronted him about he at first he denied it but then later said He was just trying to comfort himself. With sex …? And other bull 😟 I just stayed quiet and I just don’t understand why someone would do that.