Lois is ALWAYS "the one" for Clark/Superman, but for now that isn't going to happen. I think he acknowledges that at the end of SR. He'll keep an eye on her and Jason, and should be broken-hearted over her, but he should be somewhat distant for a while at least, to give her space. She has clearly said no to both Clark and Superman in SR. No stalking/sulking/excessive brooding, unless we want "Superman Becomes Batman" for the title. I mean, I love tragic dramas, but that can't go on over and over unless something with Lois & Richard is going to change soon.
SO: I think it would be OK if he had a few dates while Lois seems to be definitely unavailable. He'll always hold a torch for Lois, but since he IS supposed to be such a noble, unselfish character, I don't think he'd give up on romance entirely because of the current situation. Let his mom (Martha!) talk him out of it, encourage him to expand his horizons for the time being. He'd do it so she wouldn't worry so much. Just don't let it get to the point where he's semi-married. A few dates would be good, maybe some kissing (which he'd constantly compare w/ kissing Lois, surely), but nothing too permanent. Good: dinner, dancing, movies, outdoor activities like football games where he'd have to restrain his abilities to play with the others. Guy needs to get out...
How? Don't think we're at the point where Superman/Clark would initiate anything, but he could give someone a chance. Have Jimmy set him Clark with friends from college or from his apartment building; Clark wouldn't have much reason to say "no" since Lois is obviously (to Jimmy & normal folk) out of reach for the time being. Have a new staffer at the Planet hit on Clark. Have Clark return home to Smallville, only to run into Lana (also home for a visit). Have Lori Lemaris return and get Aquaman to show up, as someone else suggested. Need overlapping, interwoven sub-plots. SR was too simplistic.
I *would* like to see Kat Grant again! How about having her - or someone else - use a chemical on Superman/Clark that makes him temporarily forget Lois and get interested in her or another interested, available female? She could be coincidental, or she could be in on it and trolling for info about Superman or about something else going on in the film. Would let us have some <AHEM> fun scenes </AHEM> without him ditching Lois deliberately. Then we could really test his chemistry with other actresses

t: Mid-kiss or even in flagrante delicto, he could suddenly get woozy and have flashbacks to Lois, and stumble out in confusion. Later he'd have a headache and might not even remember being with the other one. This could work a lot of ways within the plot, depending on whether the other woman was in on the drugging or not.