Jake Gyllenhaal stopped "wasting time on things that are trivial and superficial" when Heath Ledger died.
The 34-year-old actor has opened up about losing his 'Brokeback Mountain' co-star to an accidental overdose in 2008 to admit it changed his outlook on life.
He said: "I miss him very badly.
"Not having Heath around is very sad because I miss his expression and miss the conversations that we had over the years.
"Knowing that life is fragile makes you want to appreciate meaningful things and stop wasting time on things that are trivial and superficial. It made me want to be more present in everyday life and be as much in the moment as I can be.
"It's made me see life as being much more precious than I was ever consciously aware of before and that has made a big difference with me.
"I try to make my relationships with people as serious and real as I possibly can because those are the moments that truly inform your life and your being."
The 'Everest' star also confessed that seeing his actress sister Maggie Gyllenhaal so happy with her husband Peter Sarsgaard and their daughters Romana, nine, and Gloria, three, has made him desperate to start his own family.
He told the Daily Mirror newspaper: "I look at my sister and see how happy she is now and enjoying her family and I would like to have the same thing one day in my life."
But the 'Nightcrawler' hunk - who previously dated Taylor Swift and Kirsten Dunst and is now said to be romancing his 'Southpaw' co-star Rachel McAdams - has struggled to find "the one".
Jake added: "It's hard to find the right person and also to be ready to have a serious relationship when you do meet someone you know you would like to spend a lot of time with and get to know more deeply.
"Nothing gets me more excited than thinking about being a husband and a father one day. There is no purpose I can see more important than that. I'm so close with my two nieces. I'd do anything for them. I'd give my life for them."