I'm curious to see how they're going to make Ben and Johnny work at this point. It's not like they've really laid any groundwork for them getting together; the one scene they've shared, they didn't even seem to like each other very much, particularly Ben who came across as hostile towards Johnny. We've then got Ben and Paul fairly loved up (well, as loved up as someone like Ben Mitchell can be), and Johnny getting interest from a handsome, professional older guy who would be much more on his level, intellectually and socially speaking, than Ben.
The one thing we know is that Paul is leaving, which does suggest that Johnny and Ben are going to end up together somehow, because god forbid a Mitchell stays single for long. But the question is whether Paul leaves as a result of something happening between Johnny and Ben, or whether the two of them only get together once Paul is out of the picture.
Personally, I would really hate to see Johnny getting involved in an affair with Ben while Ben's still with Paul, it would just be incredibly out of character for him. I do wonder if maybe now his exams are finished he accepts a date with Tom, the two of them get into a relationship, and Ben starts to get jealous. Paul could then notice, which could be why he leaves - though that doesn't sound very 'explosive' which is what we've been promised.