Now that Georgina has gotten involved "officially" with D/F, the only other f-character that needs to speed up is Jennifer. She probably has half the content of E/G. And speaking of Georgina and Jen, its good they aren't mutually exclusive now, at least going off the route selection panel. Rachel is getting her stuff started in the next update, so that'll be interesting. I'd like to see her come to the model competition to show her support to D, that can be a way to mend their relationship.
It seems like most of the disappointment is from people who want M-Sharing content. Thats understandable, but this game has always had slow progression. I do think that'll speed up quite a bit as D is more open, as we saw with Georgina, but Martin will probably be the last guy she'll get with if I had to guess.
The other two have a girl to speed things up, Olivia and Margo, who have already done stuff with D/F and they can serve as a catalyst for their guys. Really, all that needs to happen with G/O is to have another double-date and go to their place afterwards and all that needs to happen with R/M is to have another "date night" and for Ryan to stay with them instead of leaving. Martin is different, so far both he and D are curious but Martin is trying to not be a perv and he isn't going to initiate it, I'd say he even feels bad about his thoughts, so D has to do it (with F's consent).
That said, I do think being D's trainer can speed things up and some stuff that could make sense as far as building the sexual tension, which eventually turns into sex, goes.
- Swimming. Put D in a bikini and let her show off a bit to Martin. Swimming is a good way to get fitness, maybe Martin even helps her like he did with the pullups. This can also be a reason to go to the nudist beach.
- Yoga. Obviously you can get into some interesting positions with this.
- A gym that has shared showers. Squats, bench press etc.