Lifehailmartian & Bloodymary Headcanons
...While Mark is off getting them more food and David (and company) are in a hibernation period to avoid eating more of their food Grace and Rocky pick up Simon.
Simon knows there was a David in the Coalition of Iron who was a total two-faced bitch and thinks it must be the same guy he heard on the radio and either it's another trick of the eel, or Grace and the rock thing are lying about who they are and that he's free to move around (& he's really back with the COI and this is some sort of sick test...) OR Grace is genuine and David is a spy for the COI.
Simon really wants this to be real so he takes to stalking David. He's not going back and he's not gonna let the COI hurt Grace.
David takes Simon's suspicion in stride this just means he doesn't have to look far to find Simon to treat his wounds and remind him to take his meds.
That is until Simon gets mad at the doctor's clearly fake niceness, pushes too far, and discovers David does have a secret just not the one he thought.
Simon shoves him against the bulkhead and the monster shows itself, shark teeth and mutated tentacles coming out to defend him.
David quickly calls off his guard dog as he recognizes Simon is traumatized and lashing out (the same as he used to be after coming back from Syria.)
But the damage was done in that Simon saw what they were.
Simon [just survived the horrors of a mutagenic blood ocean]: They threw you in the ocean too?
David [NASA astronaut, very confused]: That's the usual way we do re-entry.
Simon still assumes David is the David he heard on the radio but that he's been chewed and spat by the COI same as him.
David is completely clueless to all this and is just glad that Simon has become more pleasant company of late.
He was wrong. It's not the COI.
No, no he won't go back...
David [uno reverse stalking]: Hey Simon, so this is Mark.
Mark: Hey man! How's it going?
David: He's from Earth. Same as Grace. Same as me... Most of me. And this is where we grow our food so we don't starve. You know not starving is important to your overall health...
Simon, traumatized, worried about their intentions for Grace initiates the thinly-veiled threats. Cue three-way shovel talk/pissing contest because all of these guys have pack-bonded with Grace, & teacher likes me best...
Grace [teacher voice]: What's going on in there?
Simon, Mark, and David [too quickly]: Nothing.
Rocky: Doesn't sound like nothing.
What Grace thinks of all this
If they are competing for Grace they're all going to lose because Rocky is already Grace's best friend. (Though he does enjoy their company.)
There are cameras everywhere on board the Mary. Grace does try to respect privacy but he can't help but be concerned about arguments brewing and he is the Captain Doctor so needs to know what's going on with his "crew." His curiosity gets the better of him when Rocky insists they were talking about him.
Grace doesn't know what to make of this. He was never the popular kid on Earth and now all these cool guys are fighting to be his friend...