What kind of therapist would advise a client that it is best to keep a secret?! Bottom line is that trust has been broken and he betrayed you.

And he ought to take personal accountability:

1. HE decided to keep it secret (he is a grown man after all, and can make decisions for himself). That is the first lie. And that is bad enough.

2. He lied a second time when he 'admitted' ONE YEAR LATER.
It is not 2 years since it happened, in December 2025 it will be two years.

3. He lied a THIRD time, when he admitted he did more than kiss someone else. Worse, he did not tell you face to face, but via a voice message?! I also wonder if he even told the whole truth this time. He may tell you later on that they slept together more than once... or there may have been others.

That IS a big betrayal of trust. He broke your dealbreaker (i.e. to never cheat).

And sorry but there is no guarantee he will never do this again. People who stray are more likely to stray again. The fact he has done this increases the probability of it happening again. Especially as he lied even when he supposedly came clean to you.

As for how to proceed, that is up to you. Can you rebuild trust with someone like that? Is your dealbreaker not a dealbreaker, then? Great that he makes you feel seen but is that enough, if you know what he can do behind your back?

You can give yourself time before making any decisions. Maybe take a break. The best may be to try couple counselling to help process this betrayal. Then make a decision.

Ultimately, the decision is yours. There are no guarantees of ANYTHING in life. His word holds no guarantee. You need to assess how you feel and go with that.