The pair made history earlier this year when they became the BBC ballroom show’s first-ever all-male couple.
However, John told Hello magazine he had expressed concern about taking part to his partner of 13 years, graphic designer Paul Atkins.
The former Great British Bake Off winner said: “He told me, ‘Don’t do it if you feel that way’.
“My emotional wellbeing was all that mattered to him and that’s one of the things I love most about Paul.
“Deep down I knew that doing Strictly was the right thing to do. It was time to flick the switch and, as Jo says every day, go for gold.”
Johannes also said he was “scared of the reaction it could bring” despite there being “no doubt in my mind that the dance side of it would work”.
“I thought criticism would come from all sides. After speaking to my therapist I realised what was holding me back was still feeling ashamed,” he said.
“Despite my fear, I couldn’t let this opportunity go to anyone else.”
John and Johannes said they have turned off most of their social media accounts in a bid to block out homophobic abuse.
John has deleted his Twitter account permanently and describes the site as “a breeding ground for toxic opinion”.
Johannes added: “I did it for the sake of my mental health. For me to function properly and give John the experience he deserves, I need to be fit mentally and physically.
“If you consider what people are saying about you on social media you would never survive an experience like this.”
However, the pair also celebrated the positive impact of their same-sex pairing, with Johannes saying it “stands for something far bigger than we actually realise”.
“There are still societies that don’t accept homosexuality and where people don’t have human rights,” he said.
“That’s one reason why it’s important to keep breaking down those barriers and people seeing John and me on the dance floor is a big step towards that. If we win, that message would be even louder.”
Read the full interview in Hello! magazine, out now.