The pair declared in 1999 that they would marry if the Vermont Supreme Court legalised same-sex marriage - with Heche declaring, "There is no one keeping their fingers crossed more than us."
But after they split in 2000, Heche began dating Coleman Laffoon, a cameraman who had worked on DeGeneres' recent comedy tour. They married in September 2001, welcoming a son, Homer, in March 2002. They officially split in 2007, and Heche began dating her Men in Trees co-star James Tupper.
The pair never married, though they had a son, Atlas, together in 2009 and separated in 2018.
Tupper has also shared a sweet tribute to his ex-partner.
Just hours before her death was confirmed by news outlets, Tupper, 57, posted on Instagram to share a tribute to the Emmy Award-winning actress.
"Love you forever," the Big Little Liars star wrote alongside a broken heart emoji. The pixellated snap shows Heche softly smiling, head tilted.
Heche's older son, Homer Laffoon, 20, issued a statement mourning the mother he shared with his younger brother Atlas, aged 13.
He said: "Today my brother Atlas and I lost our Mom. After six days of unbelievable emotional swings, I am left with a deep, wordless sadness.
"Hopefully my mom is free from pain and beginning to explore what I like to imagine as her eternal freedom.
"Over those six days, thousands of friends, family and fans made their hearts known to me. I am grateful for their love, as I am for the support of my Dad, Coley, and my step-mom Alexi, who continue to be my rocks during this time. Rest In Peace Mom, I love you, Homer."
Heche's fatal accident took place on August 5, as the fiery car crash ignited a blaze that consumed both her vehicle and the home into which she had crashed.
It took 59 firefighters to extinguish the flames, but the homeowner was uninjured.
According to a spokesperson from the Los Angeles Police Department, Heche had narcotics in her system at the time of the crash.
- Additional reporting Bang! Showbiz