Is this correct? I am really hurt when I saw her eat lunch with someon else, while I ate alone? Is the tense correct?
Someone not someon
No. You need to make all the verbs in the same tense.
The tense of your sentence, "I am really hurt when I saw her eat lunch with someone else, while I ate alone," is not correct. When referring to two past events that occurred at different times, you should use the past tense consistently. Here's how you can correct the tense in your sentence:
"I was really hurt when I saw her eat lunch with someone else while I was eating alone."
To determine the correct tense, identify the main clause of the sentence (in this case, "I was really hurt") and use the past tense throughout the sentence. In this revised sentence, both actions occurred in the past, so they are both described using the past tense ("saw" and "was eating").