does sex make a relationship last longer?

[love]

im sure we all heard about this that sex makes a relationship last. then how come there are a number of girls and some guys crying about how they had sex with their gf/bf but their relationship never lasted more than a day after they had sex? does sex really make a relationship last? nowadays i hear of relationships where the couple only been together for about a few months and they are having sex already. my friends tell me sex isn't love but yet they do it anyways. should sex and love be two different things people do in a relationship? does love really develop that fast for everyone? how come couples have sex the first few months they get together, then they break up a while later? if this ever happened to anyone is there ever a feeling of regret after the breakup?