Who may enter a love relationship with Cullen? You can enter a relationship with Cullen only if you play a human female or an elf female. In the rest of the cases, you will be able to flirt with him around, without any serious arrangements and this leads to no serious changes in relations with him.
How to build positive relations with Cullen? During all of the conversations participated by Cullen (regardless of whether you talk eye-to eye, or with more characters ), pick the dialogue options that suggest being positive towards the actions of the Templars. Also, remember to pick all of the dialogue options marked with the heart symbol.
More important steps:
- It is not too complicated to lay foundations for a successful relationship with Cullen. As often as possible, talk to him and pick the appropriate dialogue options (also, play a game of chess with him). Soon after you reach Skyhold, he should finally react to your advances, as a result of which you will kiss.
- Later into the game, you need to complete several side quests connected with Cullen (the Inner Circle tab in your journal). The first of these quests is entitled Perseverance and it is about Cullen's addiction to lyrium. It is important that you DO NOT encourage him to keep taking lyrium. Otherwise he may call off the existing relationship or the romance won't start at all, because he'll refuse to be in one with the main character.
- The second quest is Happier Times, where you accompany Cullen to the place that he has pleasant memories connected with. The meeting should end up in another kiss and you receive a present from him.
- If, during the main storyline, you have chosen to ally yourself with the mages, you get the opportunity to complete one more quest from Cullen -Before the Dawn. It does not induce any serious alterations in the relationship with him so, do not worry if you have elected to ally yourself with the Templars.