Sam Sulek fan fiction could be about various things. It might center around adventures Sam Sulek could go on, his relationships with other characters, or his achievements in a fictionalized or alternate setting. It's a creative way for fans to explore different scenarios involving Sam Sulek.
Perhaps Sam Sulek was in a relationship where he was deeply in love, but his partner wasn't as committed. Eventually, the partner left, which was the heartbreak.
I'm not sure specifically which 'Sam Sulek heartbreak story' you're referring to. There could be many people named Sam Sulek. Maybe he had a relationship that ended badly, like falling in love with someone who didn't feel the same way in the end, or perhaps there was a betrayal in a friendship that felt like heartbreak.
First, get to know Sam Sulek well. Research his character traits, his likes and dislikes if they are known. Then, think of an interesting concept, like a new adventure for him. Start with a simple plot idea and build from there.