1) We do it for "his/her sake"
A common reason for delaying a break up is to prevent our partner from feeling pain. We may feel that the decision to spare our partner's feelings is a noble choice, but in fact it's usually more damaging in the long-run. Your partner has the right to an authentic relationship with someone who wants to be with him or her. By drawing things out and wasting your partner's time, you're doing a disservice to both you and your partner.
Don't use the "I don't want to hurt him/her" excuse to avoid this important decision.
2) We forget we have a choice.
You've become a pair. You more commonly use the term "we" than "I." It takes you a while to realize that relationships aren't written in stone. Relationships should broaden your horizons and add to life's joys. When you find that your relationship has closed you off and made happiness impossible, it's time to remember that you chose this, and now you can choose again.
3) We're so invested
It's the same mentality as the businessman who keeps throwing money at a failing business: You can't stop now, after all that you've invested. This is a common but irrational mentality: The fact that you've spent a lot of time together does not mean that you can't leave in the future.
4) People expect us to stay together
Your friends know you as a happy couple. Perhaps you're even engaged, and families and friends expect a wedding. Maybe you fear you'll be judged by your community or religious organization if you don't keep trying.
Staying on account of other people's expectations is a prescription for continued unhappiness. Be true to yourself first.
5) Obsession with "fixing" the relationship
I've seen sources of relationship advice that maintain that under almost no circumstances should a couple "give up" on making it work. That's nonsense. Sometimes the dynamic between a couple can give rise to a perpetually unhappy -- or even unhealthy -- relationship.
Yes, there are countless resources that will give you advice on how to save a relationship. However, you first have to determine that the relationship has enough value in the first place. Don't go on a mission to save a relationship you don't truly desire.
6) Fear of the break up
If you're with an emotionally volatile, verbally abusive, or physically abusive person, you may be so conditioned to keep the peace that you refuse to even think of breaking up. You know you won't be able to take their reaction, and you may even fear that they'll resort to violence or self-harm (suicide threats, etc.). If this is the case, it's no wonder you're feeling stuck.
The good news is that once you bring these reasons to light, you'll realize that your excuses no longer have merit. If you decide you want to break up but still don't know how you're going to do it (or get through it), I suggest you either seek professional counseling, or get my books:
How to Break Up (for women)
How to Break Up (for men)
