Guts is purely fictional. It's a concept or character that exists within the realm of imagination and creative storytelling rather than being based on reality.
Well, in eren and annie lemon fanfiction, Eren may be depicted as having a strong, almost obsessive attraction to Annie. His character might be written to be very determined in his pursuit of her. Annie could be presented as having a complex mix of emotions. She may initially resist Eren's advances due to her own guarded nature, but then gradually give in. These characteristics are often used to create a more intense and emotional relationship dynamic in the fanfiction. However, it's important to note that this is a departure from the official story and is the creative interpretation of the fan authors.
Eventually, Eren might start to investigate the reasons behind Mikasa's betrayal. If he discovers that there are more complex factors at play, like she was forced or there was a misunderstanding, he could feel a mix of guilt for his initial reaction and relief that their relationship wasn't as broken as he thought. However, if he finds out that she truly betrayed him out of her own will, he might become even more determined to carry out his plans, whatever they are, without her.
Perhaps in this fanfic, Griffith has turned into something truly evil and a threat to the world Guts cares about. Guts, being the warrior he is, might feel it's his duty to put an end to Griffith to save others. Also, Guts could be driven by his own sense of justice. If Griffith has wronged innocent people, Guts may decide that killing him is the only way to set things right.