Obviously, it's an extreme prediction, and wouldn't be surprised if I'm wrong, but everytime he's talked about that event he has been scared/ashamed to go into detail about what exactly he said to her that he would do if she didn't pack her stuff and leave.
To me there are two possibilities, he either threatened to go physical/beat her (which I don't see happening as Melina would beat him up in any fight) or he threatened to actually kill her, which goes along with Destiny's claims that he knows she started to tell her friends she no longer felt safe there.
Again, wouldn't surprise me if I'm wrong, but this is a guy who has basically told us in extreme detail about the shameful parts of his relationship and how his wife basically got a second husband and he had to put up with it for 4 months, yet he's ashamed of something he told her? it needed to be actual threats.
(Obviously I do not think he would actually go through with the threats, but he desperately wanted her to leave)
https://youtu.be/4FZK1BdFAmE?si=d0D5XVjyNs16x_ez&t=4972 "...and when I say lose it I mean I'm going to tell you to kill yourself to pack your shit and get the fuck out of here, I'm going to stab us both like get the fuck out of..."
https://youtu.be/zVG6qt9wvHw?si=kd4tFcGoGcS-Jvmj&t=5636 "I tell her she needs a pack all her shit and get the fuck out I'm leaving for two
days, if I come back and she's still here I'm going to like—we are both—(laughs)"
Both times he's talked about this drama he's made slight reference that maybe he made a threat.