HOW CN U SAI DERE IS NO CHOISE?!Edit
Simply because there isn't a choice. It is pretty clear from the first mention that Jacob and Bella might happen that she will choose Edward in the end. Quote from the movie New Moon: "Don't make me choose. Cause it'll be him. It's always been him." (Bella to Jacob).
OK, IF DERES NO CHOISE DEM Y DOS BELU DATE JACUB AND EDWURD BOTH?!!?Edit
One sentence summary: because Perfect Sparklebutt left her, Hell's Bells dated Jacob.
But if you want more explaination, here it is: in Eclipse, we have the whole thing with Victoria. To disguise her scent, Bella has to hang out with Jacob for a bit. Here's the lovely twist before this happens: Bella goes with Jacob to La Push against Edward's will, and they hang out for fun. Eventually Jacob and Bella are alone at some time, and he kisses her. Bella hits him in the face (and breaks her hand.. lol) and Edward is all upset about this.
When this is set aside because of reasons (the books claim because of teaming up against Victoria and her newborn army), Bella kisses Jacob because of reasons (the books claim it is to protect Jacob). So the abuse victim became the abuser is what we gather from this. Where is the love triangle again?
Also: dating isn't hanging out and watching your supposed other half build motorbikes. Just sayin'. (It also isn't kissing without the other's consent or kissing to get them to do stuff.)