"Robby was somebody who was doing all these sweet things for me and saying that he wants a family and a future, and then we get off the show and all he wanted to do is party and not call me," Amanda toldPeople at the finale taping, which will air Monday, September 11 at 8PM ET/PT on ABC.
"He was like, 'I want you to be my girlfriend. I haven't had a girlfriend in a long time. Let's just go full force.' I was like, 'Okay, I'm not interested in dating anybody else.'"
Amanda had reservations about getting involved with Robby in Paradise since he's friends with her ex-fiance, Josh Murray, whom she got engaged to onBachelor in Paradise's third season last summer. Because Amanda rushed into a romance with Josh and the pair's relationship ended badly in December 2016, Amanda was looking to take things slowly with Robby.
Robby appeared patient with Amanda in Mexico, and the two kept dating in California once filming wrapped.
"I'm the kind of person, when I'm into someone, I put all my effort into that, so we tried it out," Amanda explained.
But Amanda, a 27-year-old single mom, announced she had split from Robby, a 28-year-old social-media influencer and former pro swimmer, earlier this month.
In a brief preview of the Bachelor in Paradise finale that aired last week, twins Haley Ferguson and Emily Ferguson were shown accusing Robby of cheating on Amanda, and according to Reality Steve spoiler blogger Steve Carbone, Robby was caught making out with a girl at a Zac Brown Band concert in July.
"I think we just have different ideas of what a relationship is like. Like, certain things that just come naturally in a relationship, like checking in with that person, answering when I call. There were photos of him with another girl. It became too much for me," Amanda told People.
Amanda, however, defended her short-lived relationship with Robby.
"It definitely was a real relationship. I don't know why Vinny would say that. He wasn't even in Paradise with us," Amanda said, referencing the fact Vinny got eliminated from the reality dating series towards the beginning of the season.
"We really did try in real life, or at least I tried, not sure how much effort Robby put into it. I really tried to make it work, and it didn't. If I were doing anything for Instagram followers, I probably would've faked a relationship, and that's not the case. I would never be able to do that."