General

If it wont work it should end as soon as that has became apparent, however many stay in a relationship to try make it work. In my opinion people connect or they don't. A real relationship will last beyond death.

Meh. I don't really like assigning time limits to something like that. Sometimes, mutual happiness lasts a while. Other times, it doesn't. Maybe it's luck, maybe skill... doesn't matter too much. The idea is to maintain it as long as you can and work hard towards keeping it in good condition, but don't delude yourself into thinking that you're supposed to spend eternity with every person you intend to date. That will make it extremely difficult to move on when/if doesn't work out...

Bring your partner as much happiness as you can and at some point, if you realize that you may not be the best person for the job and you cannot reach a mutual understanding, you gracefully step aside so that they can find someone else that may understand them a bit better. Communicate with your partner, maintain an understanding of what you and they want out of the relationship, and actually work towards preserving it, but also know your limits and know what's best for yourself and your partner. That's all you can really do.

My last relationship lasted about 2 years, and even then, I made sure the break-up was warm, mutual, and that I could still keep in close contact with him. Nobody's bitter, he was mature about it, and there is no awkward, "post-relationship" tension between us.

I can't drag it ti' death. I get bored of her pretty easily. So I'm more of the two month type, hit it and quit it.

My relationship with someone ended in 5 months. And it was really bad

If you really love that person, it should be until the day you die.

Otherwise, hit it and quit it qurl.