I wouldn't worry too much about her guys. Remember with Jillian (jeez, you'd think TPTB would at least give Mac's love interests different freakin' names!) - she was supposed to be Mac's new 'love interest' and they had one hug and that was it. And Stella and the Fireman was supposed to be a big thing, but she didn't even seem interested in him in Turbulence. Also, it could be a one-date, one-time-sex thing like Mac/Rose or Flack and that godawful Devon. It could even be like Adam and the awful Kendal, where there was interest but nothing happened. It's not necessairily going to be a Mac-Peyton, Stella-Frankie type thing. And even if it is, the Smacked ship is still sailing after both those relationships.
EP may be 'cooling down' or distancing MS because they want to focus on THAT storyline that is coming up for D/L, and have D/L be the main office relationship on the show (because Mac/Stella would overshadow D/L because it would be so much better).
As for Stella keeping something from Mac, which I'm almost certain now is the Greek Man, I think it's because she knows he is under lots of stress 'cause of the budget cut and the Mac Taylors case and she doesn't want to add her problems to his. One thing Stella cannot stand is to be a burden on anyone, and she might think her problems with Greek Man would be a burden to Mac. Also, she is Rambo Stella, and no doubt thinks she can deal with Greek Man all alone, just like she thought she could deal with the fire, and Frankie, and the AIDS scare. When you grow up having to deal with your problems all alone, even when as an adult you find someone you love and trust enough to let help you, it is probably very hard to always remember to let that other person help you, remember you don't have to do it alone. Mac is identical - he thinks 'cause he's a Marine he can deal with all his problems alone (Sinclair and Drew for example) but he can't, he needs Stella to be his Voice of Reason and his Rambo Stell, and likewise she needs him to be her rock, her Voice of Reason (like when she got all p*ssy with Flack and he calmed her down), her Marine Mac.
Also, Stella is probably aware that Mac and she aren't Sinclair's favourite people. If Stella is going to 'break the rules' to deal with Greek Man, she will want to keep Mac from finding out, because he wouldn't fire her, even if Sinclair told him to. He might even try to help her, and get in trouble too. Stella might be prepared to risk her job, but there's no way she'd let Mac risk his. And she could be worried that if Mac found out she's being harassed, he would go Marine Mac on the guy's ratty ass. Which would be great, but would get him in big trouble especially after Dobson. Remember - Mac told Flack that if he had a sister and someone hurt her, he'd kill them. He'd certainly kill anyone who messed with Stella, then - at the very least hurt them. Stella knows him, and so she knows that, and could be keeping him out of the loop to stop him doing that.
But as always happens with these two, they get in danger from trying to handle their problems alone, and then the other one saves them. And then there are Smacked moments.
Mac and Stella trust each other implicitly, more than anyone else, and they need each other, and they know it but sometimes they forget it for a while.
I am happy though that the spoilers suggest that it is probably the Greek Man that Stella is keeping secret from Mac, rather than Lindsay's pregnancy. It makes more sense. If she's going to hide stuff from him, I'd much rather it be something personal and serious and not to do with D/L.
Please Check the Shipper Video Thread for the Fan Vid. Thank you for watching~! 
