There are two variables: friendship/rivalry, which is a continuum, and romance status, which is a binary. So for any given LI* you can have:
Friend, Romance Active Rival, Romance Active Friend, Romance Not Active Rival, Romance Not Active
All romances become active when you select the heart icon to flirt. The paths for the romances are the same, but the actual dialogue varies based on friend/rival status. In general, strong reactions either way are better than neutrality, so in order to get a romance, work on maxing out one side of the scale by either doing things they like, or disagreeing with them at every turn.
In Act 1, pretty much all you can do is flirt**. Act 2 is where things get hot and heavy. Once you've had fully-clothed fade-to-black sex with a LI, you can't get it on with another LI unless you break up with the first. In some cases, switching your affections to another is a one-time-only thing; you can't do Fenris, then do Anders, and go back to Fenris.
As far as gifts, each person has one thing you can give them in Act 2, and another item in Act 3. Their reaction will depend on where you are on the friend/rival scale.
The most you can do in Act 1 is flirt a little. Things don't really get going until Act 2.
* For the purposes of this, the love interests are Anders, Fenris, Merrill and Isabela.
** Isabela is the exception; because of her role in the plot, her romance works a little differently. I haven't played it, so I can't tell you exactly how.
no subject
Friend, Romance Active
Rival, Romance Active
Friend, Romance Not Active
Rival, Romance Not Active
All romances become active when you select the heart icon to flirt. The paths for the romances are the same, but the actual dialogue varies based on friend/rival status. In general, strong reactions either way are better than neutrality, so in order to get a romance, work on maxing out one side of the scale by either doing things they like, or disagreeing with them at every turn.
In Act 1, pretty much all you can do is flirt**. Act 2 is where things get hot and heavy. Once you've had fully-clothed fade-to-black sex with a LI, you can't get it on with another LI unless you break up with the first. In some cases, switching your affections to another is a one-time-only thing; you can't do Fenris, then do Anders, and go back to Fenris.
As far as gifts, each person has one thing you can give them in Act 2, and another item in Act 3. Their reaction will depend on where you are on the friend/rival scale.
The most you can do in Act 1 is flirt a little. Things don't really get going until Act 2.
* For the purposes of this, the love interests are Anders, Fenris, Merrill and Isabela.
** Isabela is the exception; because of her role in the plot, her romance works a little differently. I haven't played it, so I can't tell you exactly how.