Short answer. Yes. Condonation is the first of six grounds on which a petition for legal separation must be denied. If you forgave the act you are now complaining of, the court is directed to refuse the petition even though the ground itself really happened.
What the law says
The petition for legal separation shall be denied on any of the following grounds: (1) Where the aggrieved party has condoned the offense or act complained of;
Family Code, Article 56 — Grounds for Denying Legal Separation. Read the full provision →
Condonation is forgiveness after the fact
The bar applies where the aggrieved party has condoned the offense or act complained of. Condonation looks backwards: it is forgiveness of something that has already happened, given with knowledge of what it was. That is what separates it from the next ground on the list, consent, which looks forward to conduct not yet committed. Both defeat the petition, but they describe different situations, and which one a spouse is accused of depends entirely on when the forgiveness or agreement came in relation to the act.
It does not have to be said out loud
This is the part people are caught by. Condonation is usually inferred from conduct rather than from words, and resuming marital life after learning the full facts is the conduct most often pointed to. A spouse who discovers an affair, is told everything, and continues living with the other as before may be met with this defence later, whatever was felt at the time. Trying again is a reasonable thing to do and the law does not punish it, but it can cost the ground, so the decision is worth taking with open eyes.
Forgiving one act is not forgiving all of them
Condonation attaches to the offence or act complained of, not to the marriage generally. Forgiving what happened in 2019 does not forgive what happened afterwards, and a fresh act gives rise to a fresh ground with its own timing. So a petition is not necessarily lost because there was a reconciliation somewhere in the history; what matters is which specific acts the petition rests on and whether those were condoned. Where conduct is repeated, the later incidents are usually the safer footing.
Set out the sequence before you file
The useful preparation here is a plain timeline: each incident, the date you learned of it, what you did next, and whether you went on living together. It is also worth checking the rest of the article, because five other bars sit beside condonation — consent, connivance, both parties having given ground, collusion, and prescription. A lawyer will test the history against all six. Telling the whole of it, including the parts that look unhelpful, is what allows the petition to be built on ground that will hold.