First up, Steve isn't being an asshole to Marten, he's just being a friend. Everyone has one friend like that, the person who makes a little joke about whats happening to someone. The friend who might make fun of you, but who is usually the first one by your side if something terrible happens.
As well as that, if Marten becomes angry at Steve, he isn't going to be angry at Tai, now is he? We all know Marten is a manatee on codeine, but to Steve, Marten is a guy who was recently dumped by his girlfriend, and now has to face the prospect of her dating again (remember, Steve doesn't know how messed up Dora's issues were). To make it worse, Marten knows his boss wants to be the one who goes out with his ex. That can be enough to make anyone angry. So the real question is, are we seeing Steve acting like a jackass, or are we seeing him making sure his friend doesn't do something stupid (and something he will regret) later on?