Would you consider receiving dick pics, responding and hiding it from your partner cheating?

For a bit of background:

Me (22M) and my boyfriend (19M) have been together for a bit over a year.

A few nights ago he was showing me something on his phone, when he got a Snapchat notification from a name I didn’t recognize followed by a rainbow flag. I asked him about who it was but he got very defensive. I demanded he show me who it was but he maintained that it was ”some weird guy” who had added him the day before, had also followed him on Instagram and that he did not want to open what he had sent. I first assumed that the guy had been harassing him, he had been leaving the guy on read and he didn’t want to open any of his other messages. Fine. I did however, think it was strange since we have a very clear policy of always telling the other person when someone sends us a flirtatious message. I questioned him on this point, to which he let slip that the guy had asked him some questions to which he had answered.

I asked why he hadn’t blocked the guy and wanted to see the messages. He went to block him (which would cause the messages to disappear). I stopped him and started looking through the messages. There were tens of snaps sent (you can only see that a picture was sent, not the content itself). However, after scrolling a bit further up I noticed a picture of the guys rearend as well as a pciture of his junk. To the rearend photo he had responded with something of a laughing smiley face and some text (which I didn’t have the time to read) and to the genital photo he had responded through a photo (again, could only see that one had been sent, not the actual content). After these there were tens of photos exchanged between them.

This got me thinking whether there were other guys he had been messaging. After all, he is better looking than me and the much more feminine (bring this up cause from my socials you may not be able to tell my sexualtity, while from his you can and also due to feminine gays usually receiving the most ”hit on”-action) and even I have received a few flirtatious messages throughout our relationship, which I have always showed him immediately. Meanwhile, he has not received a single one, as far as I knew.

When he asked what he could do to make it better, I asked to go through his snapchat (his main way of communication) contacts and see if there were any names that I did not recognize. Mind you, this would not have meant a huge breach into his privacy as I would not see any messages, just the names on his phone. He would not let me, which makes me think there may be others.

I have gone almost no-communication for 3 days and thinking of ending the relationship. Would this be a dealbreaker for you, considering the circumstances i.e. a year-long relationship? Would you consider this cheating?