Your best bet is to put yourself in each character's shoes as much as possible and write them doing what they're inclined to do, with commonalities and clashes arising from that.
relationships
#88: “My Anti-Queer Cousin Offered to Beta Read My Lesbian Novel”
The best beta reader for your book is one who's primed to love it, and who can work with you to make it the best possible book on its own terms.
#73: Counteracting Envy of Other People’s Success
Your feelings of envy are harming you by making it hard for you to achieve a degree of self-defined success that might lead to you feeling less envious.
#56: Showing, Telling, and Tension in Romance
Romantic tension is one of those things that's often better managed during revisions, because it's all about pacing.
#51: Writing Polyamorous Relationships, Part Two
Craft your HEA to fit your characters. Let them surprise you with the innovative solution they all come up with.
#50: Writing Polyamorous Relationships
Characters take an approach of "How can we make this work for all of us?" rather than "It's too bad I have to choose one of you."
Story Hospital 