The reasons for people to live are different. First of all you could divide the group into those believing in an afterlife and those who dont.
Afterlife-People maybe want to live not to ruin their afterlife, because e.g. suicide could get you into hell.
For those who don´t believe in an afterlife, they have something to do here, as you pointed out that may be love, relationships, responsibilities etc. Also, it maybe just the fun of living, the emotions, maybe fear of death is something that keeps you going, too.
To sum it up, there are as much answers to your question as there are humans living on this planet, because everyone living has a reason to do it, those who don´t have a reason would end their lifes, since if they fear death, that again is a reason to live.
There is also a thread about suicide here: Rationality of Suicide?