The 21-year-old model is currently dating the NBA superstar, having previously been in a relationship with the rapper, and Rocky is apparently starting to feel envious of Blake.
A source explained: ''A$AP is very aware of Kendall and Blake and it honestly does make him a little jealous.
''He has fun with Kendall but up until now hadn't really been obsessed with her or anything. He liked seeing her when it was convenient for both of them but didn't make her his top priority.''
Whereas Rocky adopted a casual attitude towards his romance with Kendall, Blake is doing all he can to win her heart and establish a long-term relationship with the brunette beauty.
The insider shared: ''Looks like it was his loss because Blake is putting in some serious work. He's into Kendall and making a big move. He definitely wants to be the only guy in her life.''
Despite their split, Rocky remains on friendly terms with Kendall and even he has been surprised by how envious her currently feels towards Blake.
The rap star has women ''throwing themselves'' at him, but he is now having second thoughts about his split from Kendall.
The source told HollywoodLife.com: ''Seeing Kendall look so happy with Blake was a bit of a shock for A$AP. He's not going to get in the way if that's what she really wants.
''A$AP has girls throwing themselves at him all the time so he will definitely survive - but seeing her with Blake has made him wonder if he blew it.''
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