Another failed relationship, why??? 
According to William Swann's Self-Verification
Theory, people prefer to receive feedback from others that
is consistent with their own self-views.
At first glance this seems normal and nothing new.
But if you read the following study, you may realize why some of us
despite going through several unsuccessful relationships still
continue to hook up with the wrong person.
In this study a group of college men were divided into either a
positive self-concept group or a negative self-concept group based
on test scores done earlier.
They were then told to interact with a group of prospective
partners for about 2-3 hours. Participants were then led to believe
that one of the prospective partners have views that were
consistent with his self-views while the other prospective partners
have views that were inconsistent.
Result
Participants with positive self-concept preferred
and chose partners that view them positively.
Surprising,
Participants with negative self-concept preferred
and chose partners that view them negatively.
Although this may not explain the whole story of why some people
keep involving in disastrous relationships but it does provide us
with a good start. For example, it is so common to hear people
complaining Why am I always ended up with guys who are abusive?
Maybe they should start looking at the problem from a different
angle. 
Swann, W. B., Jr., Stein-Seroussi, A., & Giesler, R.B.
(1992) Why people self-verify. Journal of Personality and Social
Psychology, 62, 392 401.