"I'm a private person, despite what my time on reality television might say," Barney, 55, told PEOPLE in an interview published Tuesday morning. "But I wanted to speak before someone else does and uses their words, not mine. And to speak out about it so others can see how I've taken this fight on with optimism, and the good this has ultimately brought my life."
"I think everything happens for a reason, I think your destiny is pretty much set for you, and you're here to learn lessons," added the father of three. "This has been a tough lesson for me. And I'm hoping it can be a lesson for others, too."
Barney told the publication he started experiencing symptoms in May of 2019, first noticing his salivary glands were swollen on one side. He said doctors initially thought it was an infection, but an ultrasound and subsequent biopsy revealed other areas were affected, too, including the side of his neck.
It was wasn't until he paid a visit to new top doctors that the former reality star discovered his diagnosis was cancer that it had spread into his throat, tonsils and lymph nodes.
Barney said his new doctors considered operating, but a biopsy showed his cancer was too spread out to remove through surgery. He sought a second and third opinion, but all three doctors were in agreement: He would need both chemotherapy and radiation.
He decided not to share the news with coworkers and friends until the beginning of January, when he kicked off his treatment plan. His family -- including fiancée of nine years Catushia Ienni, Judge and their three children: son Spencer, 19, and daughters Sidney, 21, and Sophia, 14 -- knew before that.
"He told me the news and we both literally started crying. I just couldn't believe it," a tearful Judge, 52, told PEOPLE of the heartbreaking conversation she had with her ex at a local Starbucks. "My first thought was, 'I don't want to take my kids to their dad's funeral,' and immediately, any ill feelings between the two of us just vanished. At the end of the day, none of that matters. All we have to do is rally together to make it through this."
Barney's diagnosis has actually helped bring peace to his and Judge's admittedly dysfunctional family. Tamra and her once-estranged daughter, Sidney, began communicating again, as have Simon and his once-estranged son, Spencer. Barney says he's also been communicating more with Tamra's oldest son, 34-year-old Ryan Vieth, whose tumultuous relationship was documented on the early seasons of "RHOC."
"It's kind of like a new beginning for me and my family. It's really brought everyone closer together," Barney said. "When I told Tamra, she said she cried for like, two or three days. Things changed with our relationship from there, in a good way. We're getting along in ways we haven't in years. And she's become close with my fiancée. And that shift carried across the board with my kids, too."
"That's what I've always wanted," he continued. "My fiancée, the same thing, she's always wanted that with my ex-wife, for the kids. The kids would prefer it if we all got along. And they see that now, and it's had such a powerful effect."
Doctors have placed Barney on an aggressive treatment plan, doubling up with radiation and chemotherapy at the same time. He goes for chemotherapy every three weeks, while radiation is five days a week for a total of seven weeks.
"The process is the real bad part," he explained. "It basically attacks all of your organs. You're like poisoned. It's been killing me. If I had a choice, I probably wouldn't have done chemo and radiation at the same time, but that's what they recommended. It's like hitting your head with a hammer and pouring gas on yourself. I was ready to end it the other day, the symptoms were so bad. It's almost worst than the cancer."
"You go in Monday, you get the chemo. By Friday, Saturday, Sunday, all the steroids are wearing off that they give you, and it really hits you," he said. "I just curl up in a ball for the whole weekend in my bed, and then pray that the truck gets off me. Because I was run over by one."
"Then they give you a shot that's supposed to help your white blood cells multiply, and that hurts your bones, so you feel like you can't walk," he added. "And then the radiation, basically they hit me in my neck, my throat, and the tonsil area. It's like a 9 out of 10 pain. It's a lot of pain."
The side effects have been just as brutal, as Barney said he's barely been able to eat. "You have an appetite but you can't eat anything because your taste buds are gone, or they taste and smell like chemo -- this metallic, disgusting taste and smell," he said. "My throat is swollen and bleeding which makes it difficult to swallow even water." He's also been experiencing constant buzzing in his ear and slight hair loss.
However, he's remaining positive. "I have hope," he said. "Doctors have said I'm doing really well so far. They look at me and they go, 'Man, you don't look like you're going through chemo.' So that's good, the prognosis is good."
"I'm a huge optimist; the glass is always half full, not half empty. And I've always been that way, the cancer just enhanced it," he explained. "I'm kind of a jokester. And everyone in my life has been so supportive and offered to drive me to treatments and take care of me, but my whole motto is, 'Don't treat me like a cancer patient because that's not how I want to be treated.' So I stay strong and don't let this take me down. Because if your attitude sucks -- if you start believing, 'Oh my God, cancer's a death sentence' -- then you're done."
"I think, if you had to pick out of from all my family, I was the right person to get it," he added. "I can survive this, at least mentally." And if he can't, he's ready for that, too.
"Listen, if it's my time to die, it's my time to die," Barney said. "I've lived a good life, and you can't do anything about that. But if it's not, then I'm going to fight this. I'm going to fight it with a smile and a laugh, and I'm going to beat it. It's whatever my destiny is."