"We'll see, we'll see how it is," Johnston, 19, said March 13 in an exclusive interview at his Alaska home with Neal Karlinsky of "Good Morning America." "We'll just remain friends for now. We're both cool with that decision, and we'll see."
For the first time, Johnston described the circumstances of his split with Alaska Gov. Sarah Palin's eldest daughter, and talked about becoming a father.
"We were just, we were in a fight," the teen said. "And trying to see if we can make things work. But this is what it kind of ended up turning into. But we'll see what happens."
Johnston said he felt 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.
The young couple's relationship came under intense focus in the heat of last year's presidential campaign, with the announcement that Bristol Palin, then 17, was five months pregnant. The revelation came just days after Sarah Palin was tapped as the Republican vice presidential candidate.
At the time, Sarah Palin announced that the parents-to-be planned to marry.
Last month, Bristol Palin told Greta Van Susteren of Fox News that the plan was still on.
"Eventually, we'd like to get married," Palin told Van Susteren. "We're focusing on getting through school though, getting a career going."
Palin gave birth to a son, Tripp Easton Mitchell Johnston, on Dec. 27, 2008.
Johnston: 'I'd Give Anything' for Tripp
Johnston 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."
"Yeah, [I'm] growing up a lot," he added. "So, it's fun. It's good times."
Asked if he felt any pressure from the Palin family, Johnston said he did not.
"No," he said. "Not at all."
Johnston Thrust Onto National Stage
Johnston first appeared on the national stage at the September 2008 Republican National Convention, which he attended with the Palins. He came under early scrutiny when a MySpace page emerged on which Johnston was quoted as saying "I'm a f----- redneck," and "I don't want kids." Johnston said his friends created the page and he had nothing to do with it.
Sarah Palin said that having a baby would make her daughter "grow up faster than we had ever planned."
Bristol Palin told Van Susteren that no one had pressured her to have the child.
"It was my choice to have the baby," the 18-year-old said. "It doesn't matter what my mom's views are on it. It was my decision."
While campaigning for governor of Alaska in 2006, Sarah Palin came out strongly against abortion and said that abstinence should be taught as part of sex education in public schools. Her decision to give birth to her youngest son, Trig, who was prenatally diagnosed with Down syndrome, has been held up by conservatives as exemplary of anti-abortion values.
Palin on Abstinence, Teen Pregnancy
Sarah Palin discussed abstinence and teen pregnancy in the interview with Van Susteren.
"You get behind that, that ideal of, yes, abstinence, you know?" the new grandmother, 44, said. "Hey, don't get pregnant. Well, get beyond that when it happens, and then you deal with it. Life happens. Life happens and you deal with it, and Bristol's dealing with it wonderfully.
"Not the most ideal situation," she added. "Certainly you make the most of it."
Last October, Johnston told the Associated Press he had been dating Bristol Palin since freshman year of high school and the couple had long planned to get married.
"We were planning on getting married a long time ago, with or without the kid," Johnston told the AP. "That was the plan from the start."
He went on to describe rough wedding plans, even naming two friends he had asked to be groomsmen.
"We both love each other. We both want to marry each other. And that's what we are going to do," Johnston said at the time.
Four months later, in the interview with Van Susteren, new mother Bristol Palin sounded more tentative about the couple's wedding plans. But she said Johnston saw the baby every day and described him as a "hands-on" dad.
News that the couple had ended their relationship first emerged last week.
Johnston told the AP on March 11 that he and Palin had decided "a while ago" to end their relationship.
The Associated Press contributed to this report.