So i tried everything and i can't get Lance's purity below 50%/45%

can i get some help pleas

You have to do a few different things to lower purity as each one that does lower it only has a set effective range . This is the route I used to get  corrupted Lance. First the kiss/ride that horse for the initial corruption, then jacking off in the evening with high arousal, then going to the bar will lower it further bit by bit, after that stops lowering it go to the prostitute with high arousal that'll lower it some more, finally catch the bandit and urge Lance to fuck him this one only works/appears when you either use the top group's choice to find the bandit or when Lance encounters the Bandit of their own free will. 

Make Lance masturbate twice to lower his purity to around 80%. Then go to a bar every day. When his purity is around 65%, go to a prostitute. Then it will be around 55%. At this time, make Lance's arousal around 80% and have him rape the bandit. Here's a tip: Before raping the bandit, if you make curse attunment and Lance's arousal around 80% (there shouldn't be even a slight difference between the two numbers), next day Lance will forcefully masturbate the protagonist and even ejaculate. If curse attunment and Lance's arousal don't match, he will masturbate but not ejaculate. It seems to be a code problem.