Fail is a mistake you learn and grow from. Quit is a fail you adopt and live with.
When things don't go as planned, it's more important how you respond to the situation than what actually happened.
Related topic: Smart Change is not the same as quitting.
SMART things to do after a fail
Study the results
Adopt the mindset to learn all you can. Get the full value of the high cost of tuition you just paid to learn some lessons.
Consider personality types, love languages, other relationship tools, team dynamics. Learn and grow through the experience.
Make choices about what you believe
As stated above, it's more important how you respond, and what you choose to believe, than what actually happened. You make the choices about what you will feel, think and believe as a result of this experience.
Act accordingly
Don't fall into the trap of doing one thing and thinking another. It's easy to do, but this feeds a powerless victim mentality.
Get congruence back between your thoughts and actions. It's important to think and act accordingly. Any amount of distance between these two creates trouble for your mindset.
Respond, don't react
You are in charge of you and your response. Don't settle for living life on the level of reacting to everyone and everything else.
Trust again
It's hard, it's messy, and yes — it may happen again. But it's worth it to process through issues so you can trust again. Living in a trust-less zone of isolation isn't a smart way to live.
DUMB things to do after a fail
Demonize the person
Some people are deviously intentional enough to scheme, plot, and deceive. Usually it's best to avoid them.
But most are living Thoreau's "quiet desperation" description of life, in some level of unconscious despair. Many are just coping with various amounts of fear — you just happen to be in the fallout zone. Consider not making it personal whenever possible.
Underestimate forgiveness and kindness
People can change. You certainly want to believe you can change, right? So why not someone else?
Do the unexpected: forgive, release, respond with kindness or concern, and offer them an alternative path forward. You will definitely wind up in a better place, and maybe they will too.
Make it all about you
You're not the only one in this scenario, or any scenario. Don't make it all about you.
Become a cynic
Neither you nor the world around you will be better off with you becoming a professional cynic. There are enough of those already. It doesn't take any particular talent, or effort, or personal growth to be a cynic.
Challenge yourself to resist taking this easy way out. Just don't throw this experience away in the trash and justify never-ending criticism and complaining. That's not a smart way to respond to a fail, whether it's yours or someone else's.
Fail doesn't have to be the end. It can be the start of something new and a better you — so learn what you can and move on.