Matthews picked the Manchester-based PA over 23 other girls during the latest series of the Channel 5 dating show, but has since discovered snaps of her getting cosy with the TOWIE heartthrob in a London nightclub days after filming wrapped in July.
"Spencer was looking forward to getting to know Khloe properly away from the cameras once they got back to Britain," an alleged friend told the Daily Mail.
"However, when he saw photos of her all over Tom Pearce on the internet literally days after the wrap party, he was pretty shocked and surprised to say the least.
"The fact she couldn't remain faithful to him less than a week after the show ended convinced Spencer there was no future together."
Evans recently told the press that she doesn't "want anything to do with Spencer", adding: "It was unbelievable to win, it felt amazing. But now we're back to reality it doesn't feel great."
She also addressed the pair's failed romance on Twitter, posting lyrics to a Drake song reading "looks like we in love ..but only on camera" and retweeting a message from a fan calling for The Bachelor to be axed for "messin with young girls head[s] (sic)".
Matthews has admitted that he found the show's failure in the ratings "very difficult" to cope with.