Honestly, I think that that too is open to interpretation.
Maybe YW was never going to go with Jo all along. Maybe his plan was to go away from it all, because he has thought multiple times by now that him staying with Jo would only ever end up hurting him. The only time he agrees to go with Jo, his inner monolugue is something along the lines of "It'll be best for TJ..." Again, they both, subconsciously and consciously, keep centering the other when making decisions.
Because we never get to witness YW having that initially planned meeting with Jo at the gas station, we assume he was going to leave with Jo. But he never really truly confirms this for Jo when they take Toby to the hospital. Jo asks him to leave with him, and he'd wait at the gas station for YW. But YW doesn't says "Ok I'll go with you" here. Instead he says "Don't worry. Everything will be ok" (or something like that I forget the exact dialogue right now from the chap).
So I'd argue there's another angle here. That it is very possible that YW was never going to leave with Jo. He doesn't falter when he asks TJ to run away with him to start a new life. There's a clear difference here. That's his real desire and plan. I feel maybe he wasn;t going to go with Jo at all. Maybe, even if TJ hadn't intercepted him and confessed, he was going to go away by himself and heal, because being with Jo would mean dragging him unwittingly into this hell of a world he has had to survive.

Ummmmmmm..... If tj hadn't come when ian was about to leave... i dont think He would've stayed for tj... Like bro you were going to leave tj here alone??
My eng is not good so pls nvm