“how can you make a character being gay IMPORTANT to the story?”
the same way tracer being an ex-pilot is important to the story. or how Winston was raised by a scientist and took his name in his honor is important to the story. or how junkrat being raised in an irradiated post-war area is important to the story. or how zarya being a hero to her people is important to the story.
do you get what I’m saying? being gay - or being bi, or being trans, or being anything - matters. it matters to the character. It’s going to effect their lives in some way, even if it’s “my jilted ex-boyfriend wants revenge on me” or “I fight so I can come home to my wife” or “we need to stop the mission for a second - I’ve been binding for 12 hours and if I don’t get a break I’m going to be way more useless to you.”
I’m not gay in a vacuum - I exist and have relationships and experiences directly related to me being a gay trans man. and that should be represented when you’re writing an lgbt character.