As this situation is taking a very bad toll on me, I've invited him for lunch to discuss what's going on. I can assume that he'd rather "live" the situation than talk about it, but that's not an option for me at this stage.
However now I'm wondering what to tell him as I really don't want to sound like I'm accusing him of anything. I would like to make him feel comfortable. Any advice on how to approach that lunch?
(I must also add that I've decided to quit this job, so working for the same company shouldn't be a problem now).