"The moment the show ended and they could finally be a proper couple and go out in public together, Matt basically just disappeared," the source told the Daily Mail.
"Given the timing, it was as if he had suddenly lost interest and changed his mind about wanting a girlfriend or something. Things then fizzled out quickly."
Chelsie was apparently blindsided when Matt broke up with her, and they have now unfollowed each other on social media.
While we don't know who pulled the trigger first, Chelsie has been super vocal about her breakup with Matt since they're split, revealing in an Instagram Q&A last week that decision to end their relationship was not mutual.
"A lot of you want to know what happened between Matt and I. I am going to respect his privacy and not go into details," the chemical engineer said.
"It's a hard situation and it takes two strong people with a strong connection to get through stages from filming to the end."
Chelsea then admitted that the breakup had been one hundo percento one-sided.
After one fan asked "was the breakup mutual", Chelsie posted a viral meme of a girl giving an 'as if' face, that basically tells us everything we need to know.
Before posting the meme, Chelsie also filmed rolling her eyes at the camera.
"It's definitely been rough," Chelsie continued.
"I do not deal with heartbreak well and yeah, my heart is broken. This sucks."