"If there is anyone who knows how absolutely devastated Diddy has been since Kim's death, it's Cassie," a source tells PEOPLE
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Between his split from girlfriend of 11 years Cassie Ventura and the unexpected death of Kim Porter, the mother of four of his children, it’s been a trying few months for Sean “Diddy” Combs.

And things got even more challenging for the music mogul, 49, when Ventura, 32, posted pictures of herself kissing a new man, personal trainer Alex Fine, on Instagram this past Saturday, a source close to the rapper tells PEOPLE.

“If there is anyone who knows how absolutely devastated Diddy has been since Kim’s death, it’s Cassie. He can’t believe she feels the need to post pictures with her new guy. It’s like she did it to upset Diddy more,” the insider says.

“The whole situation is just ridiculous,” the source continues. “There is just no need to post pictures on social media at this point. Diddy is having enough of a hard time.”

Representatives for the former couple and Fine did not immediately respond to PEOPLE’s request for comment.

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Sean “Diddy” Combs
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A second source also recently told PEOPLE that Diddy believes the singer cheated on him with Fine, who’s also a professional bull rider. Ventura and Fine have reportedly known each other for months — at least since before the couple announced their split in October.

Diddy believed “there was absolutely overlap,” said the source. “Cassie wanted a personal trainer, so Diddy hired Alex for her. Then Cassie and Alex started hooking up before her relationship with Diddy was over.”

Ventura’s Instagram post of Fine, which also included a shot of her mother from a Christmas party, came just one day after the father of six made his affection for his ex-girlfriend known.

On Friday, Diddy shared a smiling photo of the singer, in which she appeared to be taking a bubble bath.

Adding a heart emoji over the top of the image, Diddy also tagged the singer in the photo, although Ventura no longer follows him on Instagram.

| Credit: Diddy/Instagram

One day after Diddy’s ex Kim Porter’s death in November, the rapper was seen reuniting with Ventura in Los Angeles.

The singer went on to share her own heartfelt memorial for Porter on social media, during which she also praised Diddy for being a wonderful father to his six children.

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Sean “Diddy” Combs and Cassie
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“There are no words….An amazing mother to her beautiful family, lit up every room she entered and now the most beautiful angel,” Ventura wrote, alongside a glamorous photo of Porter.

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On Thursday, Diddy revealed he’s still coping with the loss of Porter, explaining that his family has helped him through depression.

“GOD IS SO GOOD. THE GREATEST!!! I’m the luckiest man in the world. The way my family has been strong has humbled me,” Diddy tweeted a shot of his mother Janice cuddling up to his twins Jessie and D’Lila with Porter.

“They have led me. They brought me out of a state of deep depression. Their strength and love brought me back into the light. I love my family!!”