Did you do the plan to destroy Tanja? If you did, then do the nice guy path not the ass hole one. Doing the ass hole one will piss lucy off and end her arc. Do the nice guy option and you can take tonja on a date where lucy is there and we'll it's how you gget lucy to fall for you.
If you trying to get lucy nice choice not bad one that includes Tanja event on revenge if you need to know how don't choose bullies route if you doing Tanja revenge this base harem everyone mc meets use nice choice killer 7 hasn't made game being relationship with one girl whatever female you pick