My fiancé’s ex keeps stalking my social media

Would like some opinions about an issue with an Ex.

My beautiful Fiances ex is always on the back of my social media. They broke up over 2 years ago, and have been friends since. I’m friends with both of them until I started seeing my fiancé. Well she asked me about it really excitingly like ‘oh my god are you guys dating? 😍’ sort of thing. Meaning she is happy right? and at the time we werent dating so I said we were just hanging out and nek minute I see all of these rude snapchats about me all over her story. Well I confronted her, asking why she was upset and I got nothing out of her but me being blocked. We weren’t dating yet and he didn’t want her to know that we were sort of seeing each other. She didn’t seem to have a problem with it when she was asking me about it? Anyway, she was the one who broke up with him - via text - and left him for another man and she is also engaged to that man now. And her and her fiancé were both friends with my fiancé. But now she has blocked both of us and wants nothing to do with us. So I really don’t see the big deal in us dating when she said she was over the relationship? Sounds to me she either still loves him or wants to keep him as a backup? Or am I the one in the wrong? I just love him so much and he loves me. I didn’t think it was that big of a deal to come between us being friends but I guess I was wrong. My fiancé says not to bother with petty people like that but i hear rumours getting back around to me that are from her about me and it pisses me off! She also looks at all my instagram stories and sees everything I type in my mother’s advice pages on Facebook. Should I be blocking her from everything too?