I had not have the time to play the new update, but you can have a loyal girlfriend if you choose carfully over the run of the game. Current arousal level (the number on the kiss lips) is more important in some situations as one might think. If current arousal is 8+, that person can be conviced/coerced/pushed/seduced into actions they would not do otherwise by you or other persons(!). So keep an eye on that number, it resets each day but only as low as the openness/slut level (the red bar) is. If e.g. Clara has an arousal level this high, keep close to her and you can keep the others away.
As for general playthrough, see some of my former posts. If you e.g. want a loyal Clara, be a decent boyfriend to her. Help her, be there for her, don´t push her towards others (this game does not cushion your decisions, if you push in one direction, don´t be surprised that it one day happens). The daring clothes stuff can be done even with a loyal Clara, this is a path of it´s own and adds to the normal playthrough, if you want a loyal but daring Clara, who likes to show off.
Don´t revisit the dreams, if you want loyal girlfriends.