Can we talk about this for a minute? Combination of facts and headcanon below.
It’s obvious Beast Boy doesn’t like La’gaan. He’s like, “Ew, stop making out with my sister, ew ew ew stop it that is so gross.” And then Superboy walks by and Beast Boy immediately looks so sad for him, because he thinks Superboy is so cool and awesome and he knows he still has feelings for M’gann. And his little face is so sympathetic, like, “Dude, I am so sorry you had to see that. I hate it too.” And he knows his sister misses him too, but they’re not doing anything about it. So he’s all, “Hey, Nightwing, we need to talk about this mission to Rann…”
Annnnnd cue matchmaker BB.