The reason he was always alone in the beginning is the reason he left.
The Hulk is a danger to others, Bruce cannot control the Hulk, therefore the Hulk must remain separate, apart, from humanity.
It was only through the huge efforts of the Avenger's team that they were able to convince him that they could prevent his rampaging.
- They worked with him to help him understand and control his anger.
- They worked with him to develop a method, the Lullaby, that would allow him to revert after a mission.
- They worked with him to develop procedures and plans on when and how he might be mobilized and recalled.
- They built Veronica, a Satellite deplorable Hulk Buster suit, so that when/if he did rampage uncontrollably they could still protect others.
Ultimately he found people he could trust which would allow him to be productive rather than destructive. It was a new opportunity for him to conduct meaningful research, work closely with others, and be a part of humanity again. This is the dream he's been fighting for, meditating for years, trying various experiments to allow him to control the transformation, and if not that, then remain in control and conscious while the Hulk.
The Scarlet Witch taught him how little all of this effort did and how easily he could still be manipulated into causing great suffering and death.
The solution has been, and always will be, to run away from society, and that's what he concluded once again.
That he did so, as the hulk, suggests that he's still very blind to how far he has come in controlling the Hulk, and how much he's throwing away by running. He should be running to his friends, not from them.