When and why did Spider-man join the Avengers?

okay i am reading a comic called marvel knights spider man and from what i read he needed help finding his aunt may in this and he never had a hint to help him find out who oldnapped her and where she was. so he went to the avengers to come and help him out but something went wrong idt they knew either so he went to the x men and they think shes dead. they were wrong and the oldnapper came forward after trying to kill him several times but he gave him hints to help stop what is going to happen and if he ever made a scene he would kill aunt may. so what im saying is he only goes to him for help and thats why he joined plus he had to beat security to get in the mansion. read it hope this helps.

Spiderman joined hes part of the new Avengers