I totally agree with your statement. I have had two experiences of ending relationships. I dealt with them in very different ways and speaking from experience, if you break up, it is for a reason and you should learn to not revisit it, as it is most likely going to end up messier than the first time around.
For me, the hardest thing about breaking up with someone, wasn't that they weren't there for me to talk to, or cuddle up with, it was that I really like doing nice things for other people, such as buying them their favorite pudding for after dinner, or making the house really nice for when they get home. Without someone to do that for, making dinner or tidying the house seemed fairly pointless. Therefore, whenever I got pangs of missing my ex, I reminded myself that it was purely selfish. Fairly soon, he found a new girlfriend and this showed me even more that us breaking up was the right thing to do as he seems happy.
The time it didn't go well - With a boyfriend I had for a much shorter time, we kind of broke up but continued to talk to each other much as though we were in a couple. We met up and shopped and walked his families dog together. After having split up at Christmas time, we then started dating again properly three months later and this took what had been a fairly amicable post-relationship friendship, and wrecked it. I found out loads of things, that I am glad I know, but probably wouldn't have bothered me had we just been friends. It was really messy and I definitely would advise against going back on the decision to break up.
If the reasons for you splitting up have not gone, then you should trust your judgement and know that something better will come along, just learn from what went wrong and try to not make the same mistakes again.