He had the same expression when he was about to make love to Lana for the first time.
Oh WOW! See that, you telling me that, gives me goosebumps! But all I had during the episode was fear. So yes, maybe it's to do with the fact that I feel bad for Lois? I have only known that level of feeling end in tragedy so it's hard for me to see it as a gift. I guess when I feel stronger again I'll try looking again to find these expressions you see in Clark.