All adventurers who are close would eventually agree to spend the night with one another, it's just an unspoken rule in the lifestyle.
Though you can just ask a girl to sleep with you on the first day, you do need to recruit her more and spent more time with her before they agree to such a thing.
Once the forbidden fruit is tasted, you can spend points to purchase more skills. Please note that there's a difference in available skills in both builds. (More info in the image)