Well, Saving Marty isn't a graphic novel. Usually, a graphic novel has a lot of illustrations and visual elements, but Saving Marty doesn't have those typical features.
I'm not sure who Marty Markowitz specifically is. There could be many people with this name. Maybe he's a local figure in a certain community, an entrepreneur, or someone with a unique personal journey. Without more context, it's difficult to tell his real story.
One common theme is the exploration of an unexpected relationship. Since Buffy and Marty are from different 'worlds' in a sense, their relationship is full of surprises.
You can try some popular fanfic websites like Archive of Our Own (AO3). It has a large collection of fanfics, and you're likely to find a good number of Buffy and Marty ones there. Just use the search function and type in their names.
In fanfiction, the Marty x Lorraine relationship is often a complex exploration. Some fanfics might focus on the alternate timelines' impact on their relationship. Since in the original movie, their relationship is quite different in different time scenarios. It's fascinating to see how writers in fanfiction expand on their connection, perhaps exploring unspoken feelings or new situations that could bring them closer or drive them further apart.
One great Buffy and Marty fanfic is 'Buffy and Marty's Adventure'. It has an interesting plot where they team up to fight a new kind of supernatural threat in their town. The characters are well - written and it stays true to their personalities from the original shows they are from.