But... Jill had to always have treated Reda terribly. He was convinced he was just a potion replacement in the beginning and nothing more. That isn't randomly given info and Jill having a knee-jerk reaction. From what we were told and sawm Reda was always treated like that (and why did no one tell him otherwise before banishment???). At no point, even the flashback where they just met and had like no interaction, did they seem to be treating him like an equal or someone they wanted around.
Also, in retrospect, how stupid was the only with him for money ex-gf to fail seeing his nearly unlimited earning potential with healer guild, even if just potion level, once he was booted from party? Do people in wherever he was have free health care for reasons of plot set up and they just didn't tell us (yet)?
I feel there's a lot being skipped here. Or I am just focusing on stupid questions.
I can only theorize rn (I doubt stuff will be explained more later on, but there's always a chance), but maybe it's a matter of Jill being fed this information, assuming the worst, and then shifting the treatment of Reda as a result? And maybe he somehow managed to shift how the party treated him too?
Actually, scratch that. While I was writing that, I took a look back and the first chapter to re-familiarize myself with the expulsion scene, and it looks like only Jill was involved in it. There was no mention of the other party members until later. From what we've seen of them, it looks like Aisha (the girl in town with him) quit basically as soon as she heard Reda had been fired, and from what she said the other girls also quit a while later.
I skimmed through the rest of it just to double check, but as far as the flashbacks are concerned it looks like the two other girls might have stayed with the party after Reda was fired in part because they were in love with Jill (or at least, Rosalie was. The only time we see mention of Nycto having feelings for Jill was when Rida himself said it, and I could easily see him misunderstanding that). Eventually, that wasn't enough to hold them together and they gave up on their love and left the party. There's nothing that shows that they thought negatively of Reda, and he even says that they were "kind and laughed a lot" in the chapter were we learn that the girls left the party. We even see Nycto teaching him how to better control his mana (and fireballing the frontliners in the process, lol) and encouraging him in one of the flashbacks. Even in the flashback you were talking about, where he first joined their party, they all seemed friendly and supportive of him, joking around and laughing with him.
Honestly, I
would say that the only real incongruity is that there's no real explanation for why his confidence was so low, but looking back at it I think I can maybe come up with an explanation for that. Back when he was being expelled, Jill said to Reda's face that he was only good as a potion replacement and baggage carrier. Rida was trying to say something about still providing assistance, but Jill just spoke over him and banished him anyway. We never really see how strong Rida was at the beginning of the story, aside from having a somewhat decent heal ability, but ever since he met Mina his mana capacity has been growing (or, at least, his mana has become less restricted), and as result he's gotten significantly stronger (remember, even
he was surprised that a whole dragon could fit in his item box, since he was expecting just the wing to go in). If we extrapolate that backwards, then before meeting Mina his item box could probably hold signifcantly less, and his capacity to heal was probably a fair bit lower than we've seen in the majority of the manga. Given that he was feeling pretty depressed after being expelled
and being Riser breaking up from him, I wouldn't be surprised if he took what Jill said during the expulsion to heart and started believing it.
The only flaw in this explanation is that Seira (the lady from the guild) said something along the lines of "they must have put those thoughts in your head so that they could keep using you", but it's not impossible to chalk that up to a misunderstanding. Maybe she heard him downplay the importance of his abilities, and assumed that his party had been downplaying how useful he was in order to take advantage of him (especially since we see that the guild considered the rest of his party to be pretty rowdy and troublesome), instead of it just being a matter of Reda not realizing how rare his abilities are (note that she never said anything about them being powerful, just rare, with them being useful implied) and feeling bad about himself bc of what he'd just gone through. Basically, it could be that she was attributing to malice (on the part of his party) what she should've been attributing to ignorance (on the part of Reda, and possibly his party too if they
also didn't realize that his abilities were rare).
That said, there's definitely a lack of any sorty of explanation for how his girlfriend went from seemingly kind and caring about him before he was even in the party (at the time he would've been a low rank adventurer, probably not making much money at all expecially since he wasn't part of a party), to being a complete gold digger who doesn't care about him at all. Maybe something to do with the bar she started working at when he was first joining the party? Either way, there's a chance that it'll be explained more when (if) the story has a "punishment" arc for her.