Oh well

I think it's a different sort of tragedy.

Well, it was an open ending so anything can happen after that last page (good or bad). Tragedy would include something...tragic, so it doesn't really fall into that genre with an open ending like this.

Is it? I thought the boss was rejecting him? He did scoot away and back up into the corner as if to firmly deny him. The black haired guy even had the look of grief and realizing he was the only one still feeling something.

It didn't seem that way to me. It was more like the usual early-/mid-drama behavior of the potential partner trying to be 'a good person' to make sure his wife and child are happy even if he himself has to refuse his true love interest's advances. That's one of the things I have seen in MANY mangas with this setting, it was the typical "But I have to think about my family" kinda expression. The coworker seemed woried and anxious, but there was o grief in my opinion. He also remained bent towards the boss in the last pannel which shows that he didn't resign or give up. So the ending, how the boss reacts + how their relationship continues remains open and to our imagination.

yea, I agree, the boss backed away.. understandable.. and actually, since I don't like cheating and he didn't say he was unhappy in his marriage and also had a daughter,... this is for the best. But why wreck our hearts with a story that can't go anywhere?:)