I think my partner might be cheating on his trip abroad

My partner traveled abroad and we have been great, he always makes sure to communicate every day and keep me updated with everything he does. But we were texting yesterday and he read my last message and went offline, initially I wasn’t mad or anything but he texted the next day starting a whole new conversation with no explanation as to why he ignore my messages and went offline. I expressed that I didn’t like how he ignored me and went offline and comes back with no explanation, he ignores my complaints and continues to ask how I was doing, I mentioned it again, he ignored it again while telling me something else that doesn’t concern it. I got really mad and called him out, that it was disrespectful and unfair, I said alot and that I was mad at him. He then said yes he agrees it unfair and said sorry about that still with no explanation, the sorry sounded like he also didn’t want to say it.
He then says I can be mad but the main thing is I get well first since I am currently sick. I told him talk later and we haven’t spoken again.
It may seem stalky but he has also gone offline again same time he did yesterday.
Usually he is the sweetest person and always gives me a heads up if he has to go somewhere, he’d even text to tell me if he is going no anywhere even if we weren’t texting. He would also always apologise if he went off without telling me prior, he has never been disrespectful towards me or done anything like this before. So I’m very surprised and I think he might be hooking up with someone on his trip.
He is the type that generally avoid trouble and having issues, he would always want to make sure we don’t have any issue, this is the first time he seems to be okay having a problem with me.
I don’t know what to think anymore, the only explanation is him sleeping with someone he met and it is a weekend.
I also have no intentions of reaching out to him but I am really hurt by his actions and I just don’t know what to think.