Why? "Where I am now," she tells the magazine. "Who he is. Those are the two big ones."
Though Wiig doesn't say much else about Moretti, 32, she does explain why she left Saturday Night Live after seven seasons in May. "I know a lot of people probably assume, 'Oh, she's leaving because she is going to be doing movies now and things like that,' which I will be," she says. "But I just always knew it was going to be seven and that was it. I think maybe if I were 22, I could see myself staying a little bit, but it just felt like the right time."
Calling her final episode "very emotional," Wiig says she just wanted to get through it without breaking down in every sketch. Because nothing says comedy like breaking down."
The Bridesmaids star has already lined up three major projects -- The Secret Life of Walter Mitty (opposite Ben Stiller), Imogene (opposite Darren Criss) and The Comedian (opposite Robert De Niro) -- but she's most excited about what's to come with Moretti, her boyfriend since late 2011.
"When you're on your deathbed," she tells Marie Claire, "you probably aren't counting the movies you've made. You're looking at the people who are around you and thinking about the people in your life, and you can't lose how important that is because that's ultimately where happiness comes from."