My boyfriend thinks I betrayed him and wants to break up

I have recently discovered that my boyfriend suffers from depression. Before that, I had started talking to a foreign friend who told me that he liked me and it was a pity that I already had a boyfriend.

As I’m still young and because I’m not sure if my relationship with my current boyfriend will last, I decided to overlook the fact that my new friend doesn’t speak the same language and has nothing in common with me.

So, I asked him to wait before I break up with my current boyfriend, as a joke.

We both knew that I was joking and my friend quickly dismissed the idea and even asked to get to know my boyfriend.

Everything was fine until my boyfriend read those messages. He got irrationally jealous, and he started saying negative things and that he wanted to break up with me.

I couldn’t just leave him like that; I knew I was in the wrong but it was the only time I have made a joke of this sort.

What should I do to salvage the situation?