Preempting the social activities you two enjoy for time with him shows a really troubling lack of respect for your relationship. Calling it cockblocking makes it sound like it's all about sex but it's about a lot more than that. If I had a best friend who started turning me down for all the things we normally do together to go instead with a new best friend who I wasn't allowed to hang with, I'd be pissed and hurt... and this isn't a friend we're talking about, it's a partner!
She needs to understand how hurtful and damaging those choices are and commit to changing her ways if she really cares about her relationship with you. Sometimes people think that an "old" relationship doesn't need the same investment of time and energy to thrive as a new relationship, but that's just not true, in fact the opposite can be true when you no longer have NRE on your side.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.