There have been plenty of women who have thrown away happy marriages very quickly because they met someone who gave them the tingles, and Diana and Felix didn't necessarily have the happiest marriage. On the other route, plenty of people have done things they are uncomfortable with because the peer group/cult have pressured them into it. Also while all the family members are immune the MC's command power, all of them were influenced when he had his awakening which made all of them malleable to his will, with Felix being the most malleable.
Which isn't to say I completely disagree with you. A bit more of a slow burn wouldn't hurt. One thing to consider though, is the game is still early in development. There are nine side characters whose content hasn't been added yet. As of now, the biggest limiting factor in game is money especially if you want all their medical cards. There are times where you have to grind money in order to purchase the items needed to advance the story. That might be magnified once more characters require items to be purchased. Also those characters will require timeslots being devoted to visiting them and raising their affection, which will be less time grinding the affection of the core characters. Once the game is in a more complete state, it may not feel as though it is happening as quickly; it may be too early in development to get a good feel.
There is vaginal sex with Victoria, Victoria's receptionist, Marisha, and the prostitute on Dark Street. Characters in this game can be divided into two categories, core and side. Progress with the core characters, Diana, Amelia, and Elisa, is tied to the progression of the main story. Based on the roadmap, it appears two main story updates will be required before anything beyond oral will occur with them. Side characters will have two updates: sex and pregnancy once the latter is introduced. Vaginal sex is likely with Dottie, and perhaps more with Victoria, next update.