Neither. Author wants it to be ais in the end.

It's Ais. It's always been Ais. Nobody but her was ever "in it", Bell has never had romantic feelings for any other girl. The anime's hatred of its own main heroine truly has been such a needless trainwreck.

What??????? Didn’t Bell get over her after she treated him like dirt in season 3??? I also heard a spoiler that in the next arc she abandons him when he has a wargame or something cause of selfish reasons

She didn't "treat him like dirt". Seriously *FUCK THE ANIME FOR THIS SHIT*. Bell sheltered a monster, which in itself is literally seen as a betrayal of humanity itself by, well, humanity at large. On top of that, a dragon-type monster- are you aware that the Black Dragon ate Ais's father in front of her eyes when she was six and then flew off with her mother? And Bell's running around basically hugging its granddaughter?

So how did she react? Well, first she reacted by going into denial, because she couldn't bring herself to believe that someone that she cared about so much would betray her like this. Then when confronted with irrefutable proof, she compared it to being stabbed. Then she fought Bell, and was eventually forced to confront reality that Wiene was genuinely just a sweet and harmless little girl. At which point the mental breakdown she'd been having for the whole arc culminated and she collapsed.

Bell finished the volume by meeting with her, telling her that he forgave her for the whole fight and wanted to train with her again. Let me guess, the anime cut that because of course they did. Well, too bad. It's all water under the bridge.

Bell has never thought of any other girl romantically, before or since then. While you were preoccupied with gushing over how sweet and adorable Ryu was as she fell in love, Bell is still thinking of her purely as a friend. He's thinking solely of Ais as the one he wants in Volume 15. In Volume 16 he rejects Syr/Freya because he already loves someone else. Clinging to Ais and then learning that she still remembers him allows him to reject Freya's charm once and for all in Volume 17.

In Volume 18, all of Loki Familia is ordered to stay out of the War Game by the Guild (because the alliance would've easily beaten Freya if LF had participated, and Oomori wanted his cheap drama even at the cost of breaking logic and believability). Ais in particular is ordered to stand down by the Guild, her familia's leadership and her goddess, then Freya calls in a favor Ais owes her and orders Ais to not contact Bell at all. If Ais had participated, the alliance would've forfeited the War Game on grounds of an ineligible player. This all causes Ais to have a second mental breakdown- she tries not to watch the War Game and hides in her room until Tiona kicks down the door and drags her out, at which point Ais ends up clawing herself until she bleeds from horror and frustration when she sees Ottar beating the crap out of Bell.

Ais loves Bell (even if she hasn't quite realized it yet). Bell loves Ais, and has since Volume 1. This has been the only pairing of the story since the Prologue of Volume 1, and this is the only one there will be for Bell. There is no harem (Ryu herself is explicitly disgusted by that idea in Volume 17). There will be no drama. There are no "challengers", despite what desperate fans used to other animes delude themselves into thinking. Oomori just likes having his MC be a chick magnet. That's it.

Bell still hasn't ended up with anyone because we are really far from the ending of the serie, but yes, Ais is the only option. He has only ever shown romantic interest in her and nobody else.

He never got over her, neither it ever seemed as such. She may have antagonized him, but she wasn't coldhearted or anything like that. She was mentally troubled and gave him opprtunities to step aside. Well, in the LN, don't know how the anime may have handled it.

There is a War Game and she does stay out, but not because of a selfish reason. Her entire familia is literally prohibited to participate. Even the top executives work to ensure that the young ones don't get involved after some negotation. She also doesn't train him, but that also isn't because of selfishness. Freya used a favor Ais owed her from when she allowed her to tran with Ottar in SO11, telling her she couldn't meet with Bell until after the War Game.

Some people either really misunderstanding Ais or some people spread lies about her😅