Yes. Do it.
WRITE THE FLASHBACK.
(in the distance, the sounds of writers crying out that flashbacks are right up there with prologues/epilogues—worthless wastes of time)
But right now I’m going to argue YES, write that flashback. Write that prologue and epilogue. Just because you write it doesn’t mean you have to keep it in the final draft. For a first draft, write them all with no regrets. The flashbacks will help you in revision. They’ll improve your character development and character arc. They are FOR YOU.
(similarly, a prologue/epilogue is usually to help you figure out your plot)
Flashbacks will help you (the writer) get to know your character. Sure, this is stuff you should be revealing through real-time dialogue and action. But the better you know their intimate histories and agonies, the better you can show who they’ve become in present day. What makes them happy or upset? Who were they close to in their childhood? These things shaped who they are today.
You’ll learn what bothers your character. What do they regret? What do they miss? What do they want? This ties into the whole swoons and wounds thing I’m always going on about.
For example, let’s say one of Alice’s favorite memories is breaking her arm when she was four. Breaking her arm?! A happy memory?! Yes, because her parents actually stopped fighting for long enough to bring her to the hospital. They worked together for her sake. So, knowing about this point in her past lets me know how much she longs for a happy family, and how she sees herself partly at fault for her parents’ later divorce—she couldn’t be the glue to keep them connected and cooperating.
Where have you been, where are you going? Who they were at the time of the flashback isn’t necessarily the same person they are now… but parts will still be the same. How good are they at letting go? Do they hold grudges? If they’re still thinking about the things mentioned in the flashbacks you write, then you’re starting to get an idea of where they’re headed. Or at least, where they might be headed if they don’t change their ways. (hint: character arc)
So yes, please write those flashbacks. Let them help you figure out your characters.
Later, there’s a pretty good chance you’ll want to cut those flashbacks (as sad as it will make you), but don’t delete them entirely. Keep them on a separate document! They’re like resources for sharpening and strengthening your character’s development and build.
Flashbacks are friends!