For context I(17ftm) have been staying with my boyfriend(16M) for the past 3 months due to my abusive parents, and both me and my boyfriend have a range of mental health issues.

Well today my boyfriend got in a really bad aggressive mood because he heard two cats fighting outside and went to look and one was one of ours, neither cat was hurt and we didn't see who started the fight but it got him really angry and he turned violent storming put yelling about how he was going to kill and gut the neighbors cat because of this. I've been around him when he gets in this state before and I know that he lashes out verbally when he's like this, ive been on the receiving end of this before and discovered that it Triggers my ptsd. When he stormed out he didn't take keys for the front gate and when he got back he messaged me asking me to open the gate for him, I told him that I couldn't do that until he calmed down and asked him politely to try and calm himself down first or to ask someone else to open for him, instead he threatened to break the door down. After that I didn't respond, I don't respond to threats and he is well aware of this. I don't know how he eventually got in but he stormed into the room and started berating me for having an "attitude" with him and started threatening to kick me out and I went into a full ptsd attack after this, luckily his dad (who I am very close with) was able to find a distraction for me and calm me down.

Once my boyfriend had calmed down we all talked about his behavior and it seemed like he was agreeing with us and everything was fine for the rest of the day.

But then a few minutes ago he sent me a message that a friend of ours sent him and asked me to read it to him because he was having a hard time focusing on his phone screen, I read it out to him a few times but a lot of parts didn't make sense to either of us so I asked him what the context of it was and he sent me a screenshot of it, the previous messages did not help to explain what I had read but near the top of the screen I saw that she had replied to one of his messages stating that he was going to break up with me. I can't see what time he sent the message so I don't know if it's something he was just saying during a fit of rage or if he actually plans to do it, but everything between us had been perfectly normal since we discussed the problem this morning.

I don't know what to do, should I tell him I know? Should I keep my mouth shut? Is there a subtle way I can let him know that I know without actually telling him?

I really don't want to lose him but this also scares me for other reasons, if we did break up it would be super awkward to be living together or he might kick me out entirely so I'd have nowhere to go, please don't think I'm only with him so I can stay here, my primary goal here is to find a way for us to move past this but given the current state of my life these concerns are very real ones for my safety as well.

Edit: I do not live in the US, I live in South africa