Jo Marney, 25, was suspended from the party after leaked messages showing her making controversial remarks about Prince Harry's fiancee Meghan Markle were published in January.
Mr Bolton is not saying that Ms Marney did not write the leaked messages but is to claim she was "stitched up" as he fights allegations of having shown "deeply flawed judgement".
He reportedly broke up with the 25-year-old - who describes herself as a model, actor and journalist - after she caused outcry by stating Harry's "black American" fiancee will "taint" the Royal Family with "her seed" and pave the way for a "black king".
However, he was seen at restaurants with her following the break-up. Asked if he was still in love with Ms Marney in an interview with Andrew Marr on Sunday, Mr Bolton said: "There are strong affections there, yes."
Former UKIP leadership candidate Ben Walker has called for Mr Bolton's resignation, accusing him of having "deeply flawed judgement".
The party is set to hold an emergency general meeting on Saturday 17 February to decide on Mr Bolton's leadership, after he refused to stand down following a vote of no confidence.
Sky News understands the UKIP leader is to claim the comments made by Ms Marney took place while she played what a UKIP source described as a "Cards Against Humanity-style game" over Facebook messenger, a game similar to the politically incorrect fill-in-the-blank card party game.
At the time of the leak, Ms Marney said: "The opinions I expressed were deliberately exaggerated in order to make a point and have, to an extent, been taken out of context. Yet I fully recognise the offence they have caused."
Mr Bolton has claimed the messages lacked context, and he told Marr "the source of those tweets has already said publicly that they were doctored" and that they were not initially public.
"The source of one of those texts, or a couple of them, has said - and they weren't texts by the way, the were private Facebook messages - that they were doctored by him.
"In the days to come, there will be more evidence being presented as to how they were obtained."
Disputing the party wished for Mr Bolton to state his relationship with Ms Marney was over, the UKIP leader added: "The NEC held a vote of no confidence for a range of reasons. The general consensus was that there was a problem with my judgement around that whole episode."
UKIP should be focused on shaping the debate about Brexit, said Mr Bolton, "not whether ot not somebody way before I met them actually send private messages that actually had nothing to do with me and I had no means of knowing about them.
Mr Bolton said it was "not the point" that the relationship was still live.