Long time no see!
After a long time, I logged in just to show my thoughts about what I think is unnecessary (and - sorry if I'm being harsh - ridiculous) uproar.
First of all, So Min and Leejoon are professionals, and are known to be very serious and commited to their profession. If both of them should promote their work, and if this requires that they have to promote the chemistry between them and their co-stars, they would and have to do that. If actors who are not single don't promote their work, be that romance or not - even if implies be friendly and make sure their chemsitry is credible, I bet directors, writers and producers won't like to engage those actors that are not single.
Second, I would like to ask if it was the other way around (that is: if it was Lee joon or any other male actor being friendly with his co-star) people will make such a uproar about it. Normaly, I'm not someone who likes to explain everything through the bias of sexism, but we can't deny that women are easier to be judged severily and to be expected/demanded to have a certain kind of behaviour, which in a man nobody will think innapropriety. In other words: people will easily say that a woman's behaviour is inappropriate while the same kind of behaviour will pass as normal if it was a guy.
Third: I watched the bts' and pics, expecting to see something strange and compromising and to my "deception" there was nothing in it that could be see as different in her behaviour from her time working with LMK. The way she behaves toward SIG is the same as her behaviour towards LMK. If we remember the thousands of "proves" showed by their shippers that they were a item - through the bts and pics - we will see the same uproar as now (but now is worst because as people knows she is with LJ, they read her behaviour as "cheating" or innapropriated or "she have to be single now otherwise she is cheating or behaving as an easy girl"). It is true that she is friendly and confortable around SIG, but IMO it is also true the same with her other co-star, who plays her older brother, and even with a guy who plays a policeman. I really can't see any difference, other than the fact with the male leads she has more time together, and obvious has more proximity. SM is known as someone playfull with her partners, easygoing and probably is doing her job promoting her drama through exposing the chemistry between them.
And now, let's be logical:
a) Lee Joon knows SM and knows that she is friendly and professional, and in spite of that, he loves her and is willing to date her, knowing how difficult it is to date a celebrity, in special when he has to be "off" and the gilrfriend has to work (on) and knows that the girl has to take all the eyes and "bashing" from the public, which is worst in the case of actresses.
b) If Lee Joon doesn't mind when she is being friendly with her partners , why should the fans demands another kind of behaviour or judge her behaviour? We don't know their relationship, and so, we don't know what LJ thinks about this. I bet he understands and accepts it as a trait of SM's personality that he loves. Because I bet he is mature, he is sure of himself, he knows he is enough of a man to her, he trusts her, so he won't be unsure of her (and himself lol!!)
c) The fact that LJ is in a special service now, allows them to be seeing each other frequentely. This means that the risk of MS time is minimal in their case. If they broke now it would be because they are not meant. And if it was the case, I bet they would have announced that.
d) SM knows very well this industry. She knows how things works to women. It would be so idiot of her if she being in a relationship with a guy, is cheating on him, or is liking another co-star, and while that puts pics and behaves in a careless way that it could betray her and attract public bashing (now and) when news about the supposed broke up/new relationship comes up!! It is soooo idiot to do it that, to me, her behaviour (the pics uploaded and so on) are evidences that she is still very much taken by LJ.
e) So, let's not be so worried and sometimes even "mean" towards them. Besides, que sera sera!!
I don't believe that I wrote so long about what I think is a silly uproar!
Back to logged out mode!
P.S.: If people knows what brazilians actors have to do, even married ones, nobary will have any worries about koreans celebrities lol