That sounds great. With the phone split screen idea, you could also have a couple other apps that fit within the streamer GF idea, like an insta type app where she posts more and more provocative stuff but still hides the full extent of her corruption, another "secret" profile with an hidden identity posting the lewder stuff, a "twitter/city message board" type app where people talk about the hot streamer girl they came across who was acting slutty, maybe even an OF later if/when MC realizes what's up where he can spend earned currency to buy pictures of his girlfriend with random dudes.
To that last point the big thing with such a setting would be that without dungeon segments there would need to be tasks for the MC to do in the overworld, where he earns money but also to give an aim to the running around the place.