OTHER: A mix of both.
Everyday people break up and they can do things to aliviate the other person's grief. But it is nothing involving mind manipulation. Specially if that other person is unaware of it.
By deleting Lois' memory, Superman is no better than the Superman who spies Lois with his X-rays vision, only by his decision and Lois being unaware.
Superman is just violating - because it is not with Lois' permission - her mind, incapacitating her to move on. Now, Lois doesn't know she and Superman can't be together and therefore is incapacitated to forget him and find happiness somewhere else. At the end of the movie, she's still in love with Superman and he's letting her believe so.
Now, Superman had different other ways to aliviate Lois' pain but opted for the one that was easier and faster for him. He could have quit Daily Planet so she wouldn't have to see him everyday, all the time. After all, he's Superman, he doesn't need to work in that particular newspaper or even work at all. THAT way he would have been brave in his actions, sacrificing himself and only himself in the process. Lois would have started to forget and, most important, to learn from her experience.
By deleting her memory Superman took Lois' right to learn from experience.
By deleting her memory, Superman just ensure he would keep his job and he wouldn't have to watch Lois' pain, which he is directly responsible of.
By deleting her memory, he basically was at the same time, relieving himself from the burden.
And at the very least he could have told her: I can relieve you from the pain, let me make you forget. It's your mind so I CAN'T decide for you; it is forbidden to interfere in human history, let alone in human minds.
But no, he decided that himself. He wasn't honest at all about it and when you love and when you have the other person's sake in your mind first than your own, you tell the otheer people, you get the other people involved into a couple's decisions. This was a one man decision.