He might become very withdrawn. Bell could start to isolate himself from others, especially those associated with Hestia. He may no longer trust as easily as he did before.
In Percy Jackson fanfiction, a relationship between Percy and Hestia could be really interesting. Hestia is the goddess of the hearth, representing home and warmth. A love story might involve Percy finding a new kind of peace and comfort in Hestia's presence. Maybe after all his adventures, he discovers a different kind of love with her, one that's more about stability and a sense of belonging.
Percy might initially be in shock. He has always trusted Hestia, so when she betrays him, it would be a huge blow. He could become very angry and feel a sense of deep betrayal. He might lash out at those around him, or he could go into a state of self - doubt, wondering what he did wrong to make Hestia turn against him.
Percy would most likely be extremely confused and frustrated. He has been through a lot already in his life as a demigod. Being forced into a marriage with Hestia would seem like another huge and unwanted burden. He may initially feel powerless against the will of the gods, but then his determination would surface. He'd start looking for ways to either change the situation or at least make the best of it while still maintaining his own identity and relationships with his friends.