This article contains spoilers for Amazing Spider-Man #44.
Marvel Comics has finally explained why Spider-Man needs Mary Jane Watson. Some people just don't seem comfortable being single, and Peter Parker is one of them. He's been in and out of relationships ever since he was a teenager, never staying single for long. Unfortunately those romances have often proved ill-fated, with Gwen Stacy killed by the Green Goblin and Peter's marriage to Mary Jane erased from history after Spider-Man struck an ill-advised deal with Mephisto.
Mephisto may have wiped the Spider-Man marriage out of history, but even he doesn't seem able to keep the two apart. Peter and Mary Jane have gotten back together of late, and in fact Peter has even picked up an engagement ring. It remains to be seen where the plot is going; whether he'll ever get his act together enough to pop the question. But this week's Amazing Spider-Man #44 finally reveals why Peter needs Mary Jane in his life.
Spider-Man is currently being taunted by a quasi-mystical villain named Kindred, who haunts Peter Parker's dreams. Amazing Spider-Man #44 sees Peter plunge into a multi-layered nightmare; when he awakens from one, he enters another in which he gives Mary Jane a phone call in the middle of the night. Peter is freaked out by the dreams, and admits to MJ that he's not at his best. It turns out Peter isn't only struggling with Kindred; he's also haunted by some words spoken recently by J Jonah Jameson. Jameson accused Peter of always pushing people away, that he pretends it's because he doesn't want people to get hurt, but there's more to it than that. Rather, Peter has come to realize it's a manifestation of how own low self-esteem; he believes Spider-Man is too important, and that Peter Parker's happiness doesn't really matter.
This, Peter realizes, is why he really needs MJ. He needs someone to give him a reason to take the Spider-Man mask off. And, although he doesn't vocalize it, Peter doesn't just need any old woman; he needs Mary Jane. She knows him completely, as both Peter Parker and Spider-Man, unlike all the other women Peter has dated but concealed the truth from. What's more, while Spider-Man puts tremendous pressure on the relationship, the fact remains MJ keeps coming back. She knows the fear of being married to a superhero, of being in love with someone who goes out swinging through the city every night looking for trouble, and yet she knows he is worth it. This is the love that gives Peter Parker a reason to take off his mask.
The future is uncertain for Mary Jane and Peter Parker. Their adversaries are powerful; Kindred knows all Spider-Man's secrets, and he is sure to target MJ as part of his campaign against the wall-crawler. Meanwhile, it remains to be seen how Mephisto will react to the two coming back together, when he exerted considerable effort tearing them apart.