First of all: it is not your fault.
It is not your job to blame yourself for the obvious wrongdoing of another. Cheating is a choice– it is a decision an individual makes, not something that they are forced to do through circumstance or driven to situationally. Any flaws that you may possess or any arguments that may have preceded cannot possibly be used as justification for such blatant disregard for honesty and human compassion. Let it be clear– they were not obligated to cheat, they cheated because they were selfish.
Whoever did this to you cared only about his or herself. They took everything that you had– all that you were (and are)– and used it as if it were nothing. Though difficult to accept, they did not value you to the extent that you deserved. They did not deserve to know you the way that they did, to understand and learn the small, personal details you may have revealed to them. More importantly, you did not deserve the disrespect, anxiety, heartache– you did not deserve to be squandered.
Perhaps this person left you, or maybe they want to remain in your life. Though the apologies may seem sincere, it is difficult to shake the doubt that this has driven into the relationship. Keep your head held high and remember who you are. Be unafraid to leave people who disrespect you– second chances are a rare, merciful thing, but oftentimes, they are spent on unworthy individuals. The decision is ultimately up to you, but I would think long and hard with a guarded heart and clear mind.
You may be tempted to think into the past– retrospective vision is always 20/20. You'll remember the bad times as well as the good. You'll feel the ever-conflicting emotions of loss, the flames of anger alongside the grief of being broken. Don't allow these emotions to bar you from moving forward.
As poet Rupi Kaur once noted, "do not question whether you were enough– the problem was you were so enough, [they] were not able to carry it." You are capable, you are strong, you are worthy. Carry yourself if the weight of who you are is too much for the weak of will.
You may begin to worry that you might never find someone to help you carry this weight, which is normal. Do not permit this worry to cause you to settle for yet another person who doesn't deserve you or make you ultimately happy. Make yourself happy for the time being.
This may sound silly, strange, and possibly outdated, but I like to think of such relationships as similar to the folk rock duo pairing of Simon and Garfunkel (you can ask your parents about them if it doesn't ring a bell). In this 60s band, it is blatantly clear that Paul Simon was the primary talent of the band, while Garfunkel contributed to lesser extents (in many opinions).
My mom used to always tell me that Paul Simon only paired up with Garfunkel because he was initially afraid to perform on stage alone. When the two eventually split ways, Paul Simon thrived and maintained an extremely successful solo career– Garfunkel plodded along, though did not gain nearly the same amount of accolades and individual success and faded away over time.
What I'm getting to with this story is that we should all strive to be a Paul Simon of any ruined relationship– especially ones in which we've been cheated. Sure, performing onstage alone is scary. Own that fear. Rock that solo career the best way you know how and thrive through personal confidence and success doing what you truly want to do around those who actually care for you. You didn't lose anything but a person who did not deserve to be alongside you in this performance.
Finally, don't be ashamed to reach out to others. In many cases, your family and friends will be more than willing to support and love you during a time when you feel unlovable. You're not alone– this has happened to people who came before you and will (unfortunately) most likely happen to many in the future. Take solace in the fact that you can utilize this experience to grow stronger in your judgment of character and ensure a better situation for your future.
You were wonderful before and remain wonderful. This one situation, a person's mistake, does not define you. Stand tall because you are above this. Better times will come– I promise.