Life is challenging. Relationships are challenging. It's easy to say this; easy to admit this; yet, sometimes, it's not so easy to accept this.
Living for what "could have been" means that you are not living for what "truly is." It is so easy to get caught up in imagining what the perfect relationship would be. When these mental constructions do not coincide with the experiences that are actually occurring, it can be so easy to feel negative emotions: anger, frustration, annoyance, disappointment, judgment. While these feelings are not ideal, it is important that you learn how to deal with them in a healthy, meaningful manner.
Other than the negatively charged emotions, another downside to living for what "could have been" is that you are missing out on reality; you are losing attention to the present moment and failing to practice mindful awareness. You are creating a life that is full of hope and despair for a reality that does not exist while simultaneously neglecting the real present.
In terms of relationships, it can be really easy to remain involved with somebody that is not living according to the standards and expectations that you imagine. While nobody is perfect and striving for perfection is not healthy, it is equally detrimental to both you personally and your relationship as a whole to remain involved when the reality is not aligning with what you wish it would be.
There comes a point when you are aware that you are sticking around for a fictitious reality (pretty oxymoronic, huh?!) and it hurts to have this realization. Yet, after some time, it is so beneficial for you to have this realization because you now are aware that things are lining up. This gives you an opportunity to make a change in your life and create an overall more positive lifestyle. Initially, it may not seem like a positive change; however, in the long run, it will. Your ability to identify this is liberating because it allows you to change your perception and develop a better focus on the present.
Remaining in a relationship that is more positive in terms of what it "could be" when compared to what really is introduces a potential plethora of problems. You fall into a weird scenario where you are living in a fantasy by rules of that fantasy; thus, you are disconnected from any experience and acceptance of what truly is.
Trust me, it is definitely hard to do; however, after you do it, you will feel this tremendous amount of liberation and in the long run, this will be better for you.