Levi Johnston, 19, told ABC's Good Morning America in a segment to air in the US on Monday that he and 18-year-old Bristol Palin broke up after a fight "a week, two weeks ago" and had tried to "make things work."
The two are the parents of an infant son, Tripp Easton Mitchell Johnston, born on December 27.
"But this is what it kind of ended up turning into," Johnson said in an interview from his Alaska home. "But we'll see what happens."
Johnston also said they needed time to grow up before following through on marriage plans.
"It's just us not, me not being mature enough, or something, and having a kid and thinking ... it could be better - better for us to separate for a while," Johnston said.
Sarah Palin announced her daughter's pregnancy days after being picked by John McCain to be his GOP vice presidential running mate. In September, Johnston appeared at the Republican National Convention with the Palins.
Johnston said he sees his son regularly and described how becoming a father had changed his life.
"I'd give anything for (Tripp), to be with him," he said.
"(There are) a lot of changes when you're a father, when you hold him for the first time, you know. I don't do a lot of things I used to anymore, I'll tell you that."
