Ending a relationship is never easy, no matter how impossible and frustrating it was. Many people come to therapy to find an answer to the question - should I stay, or should I go? Sadly, therapists can never provide a definitive reply as each and every one must decide for themselves. However, there are some tips that could make your decision easier.
One of the most frequent reasons people start to think about leaving is betrayal. Once one of the partners cheats, the other one is left wondering whether the relationship is still something worth investing in. Betrayal is also one of the most difficult issues to overcome as it undermines one of the fundamentals of a good relationship - trust. If cheating is a one-off thing that happened in specific circumstances, then I would say it is still worth considering staying with a partner and working on how to regain trust and make the relationship stronger. If it is a regular occurrence, then I would certainly leave. Especially if you value loyalty and faithfulness. You know what they say, "once a cheater, always a cheater".
Another reason why splitting up is brought into consideration is violence of different types. Violence is where I draw the line. Even more strictly than with cheating. If you're exposed to any kind of violence, especially physical violence, there's not much to reflect upon, really. You pack your bags and leave, or you kick your partner out the door.
Sometimes you and your partner simply grow apart. This applies to long-term relationships in particular. If you feel like your relationship is no longer in line with your values, interests, needs and desires, you have the legitimate right to leave. But before you do, assess how you contributed to the relationship getting into a dead-end. Perhaps your partner too would like to go in the same personal growth direction as you, but doesn't know how to go about it.
If you feel bored in your relationship, or suddenly start getting frustrated for silly reasons, it might be time to take a look in the mirror and check whether you're projecting your dissatisfaction with yourself onto the relationship. It often happens that we project or transfer our grievances about XYZ onto our partners and blame the relationship for our misery.
Should you fall madly in love with someone else, well, tread with caution. Everything that sparkles isn't gold. The shiny, sparkling and exciting new partner might not be as fabulous as you imagine them to be. Also, if you've had a couple of relationships under your belt, you know when you're just smitten with someone and when you're developing real, deeper feelings.
One last advice - when you know that leaving is the right option for you, you feel it in your gut. Sure, it helps if someone else whose opinion you value confirms it, but... trust yourself first and foremost as it is you who will have to live with the decision you make. And remember, you can always take a new decision if the last one turns out to be a disaster. Take responsibility for your life and make the most of it!