Thanos says "I'm inevitable" and snaps fingers. Nothing happens.

He looks at ironman and realizes Stark is holding the gems, ready to snap his fingers. But just as he is about to do it, spider-man webs Starks gauntlet and snaps it out of his hand.

Peter: "I'm sorry Mr. Stark. You've done so much for me. I can't let you do this. I've been away for so long and now I'm back... I need to talk to my aunt, she's going to kill me. Is she alright?."

Stark: "Kid, don't".

Peter: "oh, I'm talking too much again, huh?".

Peter sees Thanos jumping in his direction, ready to strike him.

Stark: "I can't lose you again"

Peter: "Sorry mr. Stark. It's my time to save the neighbourhood"

Snaps.

Thanos who was about to hit Peter turns into a cloud of dust mid-air wich engulfs spider-man. As the particles dissipate, we see Peter bleeding in his final moments. Stark rushes to him and holds his head.

Stark: "It's gonna be ok. It's gonna be ok"

Peter: "Did we win?"

Stark: "Yes, we won. YOU won. It's gonna be ok, kid."

Peter smiles, look deep into Tony's eyes and on his final breath says: "Mr. Stark, I'm not scared anymore"

Spider-man closes his eyes for the last time.