Leni's boyfriends dump her because she doesn't put out. But it's not that she won't it's just she just doesn't understand sexual innuendo. Gavin dumped Leni when he told her he wanted her to ride him untill his pelvis was broken and Leni proceeded to put a saddle on him and entered him in a bull riding tournament where he was hog tied by 10 different cowboys and trampled by a bull

The funny thing is this is probably not that far from the truth. It's implied Chaz dumped her because she couldn't understand when he was flirting with her