Peter may try to get Tony's attention back. He could show off his own skills or achievements in an attempt to remind Tony of his value. For example, he might go on a solo mission and do an amazing job, hoping that Tony will notice him again.
If he's unable to avoid it, Tony would be extremely conflicted. His face would show a mix of horror, guilt, and anger. He might yell at Thanos, blaming him for making him do such a cruel thing. After pushing Peter, Tony would likely be in a state of shock and self - loathing, feeling like he has failed Peter and himself.
He might be initially confused. Sasuke is not used to Sakura ignoring him as she has always been somewhat persistent in her attention towards him. So, he may be at a loss as to why she is suddenly acting this way.
Perhaps Tony, knowing Peter's character, is somewhat expecting the interruption. He might have a wry smile on his face and then listen to what Peter has to say. He could also play it cool and make a joke about Peter's eagerness to interrupt his meeting, while still giving Peter a chance to explain his reasons.
Peter might be initially shocked and a bit scared. After all, Tony is like a mentor to him. But then he could become defensive, trying to explain his actions or point of view.
Peter could respond with a bit of humor. He might make a joke like 'I'm not a baby, Mr. Stark, I can handle myself!' while secretly enjoying the affectionate name. This would show his growing confidence in his relationship with Tony, being able to tease him back.
Maybe Tony has a special interest in Harley in the fanfiction. His focus is completely drawn to Harley, so he ends up ignoring Peter. It could be that Harley has some unique qualities or abilities that Tony finds more appealing at the moment.
Peter could also be a bit annoyed if it's not a good time. For example, if he was really focused on a test or a lesson he was interested in. But still, he'd probably answer because he knows Natasha wouldn't call without a good reason. He might give her a look that says 'this better be important' while trying to listen to what she has to say.
Tony could be initially shocked. He might not understand why Peter would run away, especially if they had a good relationship before. He'd probably start searching for Peter right away, using all his resources.
Peter might be embarrassed at first. He's been idolizing Spider - Man and now Tony, a real - life hero - like figure, knows about it. But then he realizes that Tony could be an even greater source of knowledge and support, so he becomes more open about his love for Spider - Man.
Peter is likely to be in awe. He might be a bit nervous at first, but also extremely excited. He has looked up to the Avengers for a long time, so meeting them would be like a dream come true. He would probably be stuttering a bit as he tries to introduce himself and show his respect.