I think the others have elaborated well on how he doesn't have any reason to be happy with Archana after what she's done to him. Also, its not like she sat there by her own very happy choice, she didn't have her heart in it.
Another thing is that the whole character of Manav is generally a serious person, and if you think back to his pre-Archana days, he had pretty much the same seroius/somber expression. These days he's in his depressed mode, so he kind of wears an expression like that all the time, so I don't think it was really directed towards Archana anyways.
Edited by toothbrush13 - 16 years ago