I will admit that this comic did NOT change my life per se, but changed my thoughts on the characters and stories of my hobby.
This was one of the first comics I read that picked up dangling threads from other stories. It had lots of "guest-stars" and was worthy of being a "larger" issue.
Avengers #200 had come out in the summer of 1980. In that story, super-heroine Ms. Marvel suddenly found herself pregnant. She undergoes the whole 9 month pregnancy in the matter of a few days. Her baby is born, grows to adulthood (calling himself Marcus) and seemingly poses a threat to the Avengers.
While the story has subsequently garnered A LOT negative press, it ends with Ms. Marvel (Carol Danvers) joining Marcus in Limbo.
Sometime later, Avengers Annual #10 came out. The gist of the story is that Ms. Marvel, in limbo, under Marcus' control, got to watch as Marcus' misalignment with the time stream caused him to age rapidly and die, leaving her stranded. Somehow she returned to our dimension, but upon her return Rogue stole her powers and memories, leaving her a miserable, empty, friendless shell. Therefore she attempted to throw herself off the Brooklyn Bridge and would have died but for Spider-Woman's intervention.
But the part of the story that changed my thinking was that the Avengers had failed Ms. Marvel.
It rocked my world.