Danny Saucedo and Eric Saade are absolutely not straight. Neither is Anton Ewald. Danny has talked about thinking he was gay (!) and his need to be Catholic, and Anton claimed he went through a period with a similar struggle at the same time he was drugging himself. Eric is married now but he has not only kissed Danny in public over and over but has been seen doing this off-camera with other guys. I don't know if these guys are more gay than bi but their wanting to be famous and accepted explains a lot, especially in Sweden. Of guys in this group of Swedish pop stars only Victor Frisk has come out as bisexual (and also somewhere on the bipolar scale).
Sweden has a relatively good record on gay issues, but as a Swede I can tell you being different is not easy in Swedish society. Consensus and being part of the norm very much affect Swedish consciousness. If sexuality is your issue and you see yourself being accepted in the position of the happy Swedish family with kids, that is where you do not rebel but fuck guys on the side. I'm out, go to pride etc. but my issues are professional and struggling with the lack of education of so many of my colleagues and I am constantly censoring myself to fit in. And I have been kissed and flirted with by "straight" guys (including at work) when they're drunk at some party or function. Most Swedes at least in some ways really do not want to be seen as contrary at least in some way in normal life.
Benjamin may be truly bi and the girlfriend real, but from all the signs (including from his own mother) I'd bet he's gay-leaning-bisexual.