the choice of a route is made by the amount of times you do naughty choices or good choices for Anna. The first to reach 10 pts locks it. Also, no, even if Anna is on her Pure route you can still share her with Josef and Adrian, and also other characters too like Phoenix. the only main difference between Lover and Slut is, the outfits inside the house, the fact also that Anna will not accept to do "quickies" with you in the kitchen in Lover route, she also will not allow for Gangbang at the Starcon event or groping by randoms in the park, and also she will remain in the Flower shop working there despite making billions of money everyday thanks to Starmaker... ah yes and she wont accept Nude photos at the beach... Other than these (at least so far) the sharing routes wit other characters can still be done with either routes. Honestly i have been making her into Slut route but refusing to share her with everyone and also not choosing her to be groped or do the gangbang at the Starcon, thus making her my personal Slut lover!