Currently you are able to watch "Domestic Girlfriend" streaming on Crunchyroll, HiDive or for free with ads on Crunchyroll. It is also possible to buy "Domestic Girlfriend" as download on Google Play Movies.
Natsuo is a high school boy who is experiencing the crushing despair of unrequited love. To make matters worse, the person he is in love with is his teacher, Hina. In an attempt to lift his spirits, he attends a mixer where he meets a girl named Rui. The two sleep together, expecting never to see one another again, but fate has other plans. His life suddenly becomes more complicated when his father comes home and announces he has remarried a woman with two daughters whom Natsuo has met before: Hina and Rui!