So, my question is - do we really have to allow our second halves to change ourselves to make the relations bearable?
Of course not, but then I'm not you.
Would you really be happy with having to change the way you are to suit someone else? What was so wrong with you ( or anybody else ) that whatever they saw in you in the first place needed to be changed? If change is required to make the relationship bearable, then it can't have been that good to start off with!
This doesn't mean that you can't compromise on things though, neither of you are going to agree on everything, and you both have to be open to discussion.
So many people constantly look for something else and break up because their expectations don't match to their experiences.
This is true, and maybe some people are unrealistic about relationships. If someone sets their standards too high, they are always going to be disappointed.