The problem of finding new situations and twist on tropes is common to stories of all genres, not just Romance.
I would reccomend "Story" by Robert McKee if you really want a strong framework for creating a series of events that force character development.
The way to have "new situations" is to make them very specific to your characters and setting (one affects the other and vice versa). This means knowing your characters and setting deeply!
If you have a commanding knowledge of your world, then coming up with situations us easier cAuse you know how your characters will react and what the limits are on what they can do ba cause of their setting.
Furthermore, to plot and create a series of Events (that is defined as Scenes in which a significant, however small, change occurs) you must continually deny your principle characters what they want. That is the basis of ANY good story. Characters ARE Plot. One thing can't change without affecting the other. A story ought to be so well interwoven that the question of "plot-driven" or "character-driven" is unnecesary.
To add pressure, simply ask after a character makes an action expecting a helpful result from their world: What is the opposite of that? What do they NOT expect?
Then find a way to make that happen and force the character to try again, having faced this difficulty.
Do this again and again. Only when, and not until, you reach the end of the line, the last possible thing a character can do, will the character reveal who they are.
Because the character is not what you can observe and describe about them (that's Characterization). Character is their Decisions made under Pressure. Think of what it means to 'have good character'; it's like that. The actions you take show the world who you are.
So when you're crafting the story based off your premise or inspiring seed of an idea, decide your setting and the characterizations of your cast. Then give them obstacles to the stuff they want, pull the rug out from their feet. Don't make anything too easy for them until they've earned it.
The journey to overcome those problems is what makes for a good story and good suspense. You always want the readers to ask "what's gonna happen next?!"