Submissive argument

I engaged to my submissive and we just had a fight. I had told him that I had been fantasizing a lot lately about the idea of another to join us. As this had not entered our initial agreement, we agreed to discuss the matter. A few days past and he told me he had some concerns. I was more than willing to discuss these issues with him until it became apparent that he has some trust issues due to an old partner cheating on him with someone they had previously been with as a couple. He did not see what he was doing. His anger got the better of him and a fight broke out. We argued for a while, (maybe 2-3 hours) but by the end of it I had shown him by his own words that he believed I would in fact cheat on him. At first he begged me not to push him to admit to it but I needed him to see that he was showing a lack of trust and disrespect to me. His argument collapsed and he realized his mistake.

Now I am faced with trying to punish him in an appropriate way but even more complicated is that we are currently not in the same country. He had to return home and I am not due to go out there for a few months so I am unable to perform most of our usual punishments. He regrets his actions and I had to very clearly and strongly command him that he is not to punish himself and that he will not be punished while he is so upset. I understand that this was partly my fault that it happened in the first place yet what happened requires a firm punishment but this is far more than I ever expected from him and want to ensure that his punishment is both suitable and adequate but have never dealt with something quite so severe before on top of the fact that what ever punishment he receives must be carried out by him, observed on video call and not raise any questions with his family (they know we are engaged but not our lifestyle). I would be grateful to hear advice from both sub and dominants or any ideas on what punishments could be applied.