I guess if you are able to not only alter your memory but also the memory of those around you you change the past practically, because no one would know what really happened... and both would have a changed memory!

What you are describing actually happens as a defense mechanism, people get heartbroken and then their minds sometimes change and they start to wonder if they ever loved that person, realizing in the end that they didn't (sometime they did, but it's easier and better to lie to yourself then to see the truth)