As the title says... 

So i've been friends with this guy for around 3+ years.
We have always gotten along, and had a bit of a flirtatious relationship. This past year we both figured out we had started to grow feelings for each other, and we had plans to meet and spend time together this summer (it's long distance but our countries are basically neighbors, so we figured its something we really wanted to do this summer)

before we could plan stuff, he got really busy with work, which was fine, i knew it was important for him. I stayed busy with my DBT treatment aswell. I thought things were fine and that we would talk some more, once we both got vacation, but we never got that far haha.. 

Yesterday he wrote in our friend group, groupchat, about how he had, had a really tough week, and that he slept with a 17 year old new hire at his job, while they were both drunk. 

I'm not mad at him, because we werent exclusive, and he can technically do what he want. What hurts the most is that he wrote it in the groupchat only, and that me and him didnt have a chance to talk about it (he hasnt messaged me at all so idk) im just really confused because he called me his girlfriend at one point, and now its like im not even involved in his life.  He says he feels like he lost a lot of respect at work and rumors are going on, so he is obviously not happy about what he did. I feel like i should support him through this, but i also want to tell him that i didnt think it was okay... i dont want to make the situation worse for him.

So yeah i would really appreciate some advice on how to approach this. Should i just expect that me and him has nothing going on anymore, and just leave him be..
Or should i support him? What i want the most is tell him some supporting words and then let him know im done with him as a potentional partner, but i really dont know what to do.