The boyfriend angle isn't realistic. Loki would never ok Ais dating a Freya Familia member, especially now that she is furious with Freya. The other part is less unrealistic but one could make the argument that hurting Bells chances in the war game hurts the Loki Familia members chances at winning which effectively is bringing them into the favor which would brake the terms of the agreement.
Personally I think there are 3 possibilities for what happens with the favor.
Loki finds out about it and demands that Freya release Ais from the obligation if Loki's side wins the war game.
Freya tries to use it but is turned down by Ais due to the stipulation
(Personally I think this is the most likely outcome) One of the Freya Familia members suggest to use it and Freya shoots it down realizing that they can't sue to the stipulation.
The reason I think the 3rd option is the most likely outcome is due to the fact that I think Freya will have a redemption path in the future and the favor seems much better used as a tool in her redemption in the eyes of Ryu and Bell (like if Freya were to use it to ask Ais to save Bell or Ryu in the future) under those terms I would even bet some Loki Familia members would overlook the stipulation and help.