Struggling With Supporting Partner in Difficult Times

I’ve only just recently started to suspect that I’m on the spectrum within the last couple years or so. I’m 33 and have always known I was different in multiple ways and it’s adversely affected my friendships and romantic relationships. I struggle badly with processing emotions and social communication. I will say things that sound rude or offensive or just don’t make any sense and don’t match at all what I mean. I’ve been with my boyfriend for 5 years and we’ve struggled with communication all throughout. Tonight, while I was on the treadmill he just came in and non-chalantly told me his grandpa might have cancer. When he told me, my brain just kinda froze and I said “why couldn’t you have told me this earlier? I wish you hadn’t told me this while I was working out.”- I wasn’t upset at all but what I meant by this was I wish he’d stopped me or sat me down and had a conversation rather than drop a bomb. I get now why my words sounded awful and could’ve been interpreted badly. After he said that, I was trying to figure out if I needed to turn off the treadmill and talk to him but he just said oh well I’ll talk to you about it later and just made it seem like it wasn’t a big deal. He didn’t sound upset, he said they don’t even know if it’s cancer yet, and then he walked off and played with our cats. He acted like everything was fine. Then later he comes out of the shower and is extremely upset about how I reacted and said it felt like i didn’t care when I do very much so. I tried to explain that I’ve never really been around death and don’t really know what to do in this situation and it takes ia very long time for my brain to process that someone is DYING and then it hits me all at once when it clicks. I apologized and also explained that he seemed like everything was fine so that made me think everything was fine so I continued with what I was doing. He yelled and said I don’t care about anyone but myself even though I apologized and recognize that my reaction was terrible. I don’t feel like a selfish person…I just didn’t know what to do and still don’t. I’ve gone through life basically copying what other people do in situations and since I’ve never been in a death situation I have nothing to go off of. If anyone can help me understand this that would help. I feel like a terrible person. I want to help him but don’t know how and don’t know if I even can. It feels like I’ve betrayed him. I’m also questioning if I’m the right person for him and feel inadequate for anyone really at this point.