There are times when I'm asked by a girl if I want anything from the coffee store when she heads downstairs to get herself something. Most of the time I'll say yes to a tea or something. I do this more so in the mindset of having her invest in the relationship. Nevertheless, I still feel a little lost. Would asking her for a cup of tea be conducive to the goal of having her invest in the relationship? Should I return the favor sometimes? What are other ways I can promote the investment?

There's another chick that would be down with dropping off food for me at my house. I'm more interested in getting that food than fucking her though. She would be very enthusiastic about getting me something that costs money. i.e. I mention how I like X item. She'll make some mention about getting it for me. How can I use this relationship to further improve my understanding of having the girl invest in the relationship?

I'd really like to consolidate an understanding of being a gatekeeper of commitment.