I think a huge reason why relationships don't work out in today's world roots back to a lack of self-evaluation and rushing into something society deems ideal. Too many young people give in to the pressure of the "need" to be in a relationship before becoming independent as an individual first. This may be an unintentional weakness, but the reason why many relationships don't work out in the long run.
Ask yourself these questions: What is it you look for in a relationship? Honesty? Trust? Good communication? Emotional support? Someone to lean on? A leader? A connection of values?
…are you all of those things? Or could you be to someone else?
If you are only some of them, or would not be able to provide everything you look for in a relationship for someone else, then you are not ready for a relationship.
Jumping into a relationship without emotional stability with the hope that someone else could provide the stability you've been searching for all this time puts too much pressure on the other person. Whether your realize it or not, it strains the relationship and causes tension to build until the relationship is no longer functional.
Solid relationships are formed when two WHOLE people come together and are able to provide and support the other person. A relationship can only last when two people are able to build each other up. Building each other up is not possible if one person is always depending on the other to fill a hole in his/her life. This kind of relationship does not grow or bear any fruit. It stands still with the possibility of falling apart at any moment.
Don't get me wrong, relationships can be extremely fulfilling and a gateway to shared happiness with another individual… but what is the point of entering a relationship too soon if the potential of it not lasting is there?
Also, a relationship is not necessary to be happy in life. Too many people believe this to be the case. If you can't find satisfaction within yourself, how could you satisfy another individual to the best of your ability? Relationships are not about you, they are about the other person.
Whether you're in a relationship or not, I think we all need to re-evaluate who we are and where we are headed in life. Self-improvement is never a bad thing. And we all need to improve in certain areas of our lives.