There are really four things needed for this trophy.
1. Don't sleep with Lady Stephanie. During the quest "At Your Service My Lady" at the end of the quest refuse to put on the shirt. Or simply skip the quest.
2. Don't sleep with Theresa. Simply avoid doing the "Go See Theresa" quest until after you have this trophy. The quest can be completed at any time.
3. During Mysterious Ways do not get drunk with Father Godwin. Your best bet is to pass a persuasion check, but if you cannot don't meet him for drinks and find a different means to complete the quest.
4. Don't sleep with the bath girls. Simply never select the option to buy a girl and all that comes with it.
There is one other quest, Playing with the Devil, that I have seen noted as not voiding the trophy. However, I would just not risk it as the quest does involve some debauchery.