Would you be mad if your best friend befriended your husbands ex?

I’m gonna attempt to not make this post too long.

This is gonna be somewhat of a rant I only have a few minutes to type this out before I have to get the kids ready. Sorry if it’s hard to follow.

My best friend and I have been friends since elementary school. Since last year she has been hanging out with my husbands ex a few times a week. I got married at 18 and started having kids. She’s still single and goes out often. Now that I am a mother of 4 (youngest is 1) we don’t hang out as often but used to talk daily. My husbands ex and and my best friend have a mutual friend. Since last year my best friend and my husbands ex have been hanging out pretty frequently. It feels like my best friend is doing this to spite me. My best friend always spoke on how she felt awkward hanging around a girl who was a serious ex of my husband. After I had my youngest I had some postpartum depression. My body didn’t snap back like it did with the first three and I was slightly overwhelmed with 3 kids and a newborn. Throughout my postpartum period I didn’t return my best friends phone calls or even really see her because I was feeling down about myself. My best friend would text me and make comments about me forgetting about her and only caring about my family. I just laughed it off as her joking but now I feel like she was serious. When I stopped actively talking to her daily she befriended my husbands ex & started doing questionable things. Like after I expressed to her how I didn’t like my postpartum body, she would snap me pictures of my husbands ex in a bikini. She would literally send me snaps of her shaking her boobs in the camera knowing that my husband was probably with me. As I started to distance myself more she would hang out with her more. My best friend used to tell me how lucky I was to have found the love of my life so young and be able to start a family. I used to think she was genuinely happy for me but now I think she had some jealousy brewing. I stopped returning all of her texts and calls all together. Last weekend my best friend was drunk texting me telling me how much she misses me and wants to see the kids. I ignored it but It got me thinking. Am I in the wrong for feeling upset? I never told my best friend how i felt. I had this feeling that my best friend would run and tell my husbands ex that I was jealous or intimidated by her & I literally used to tell her everything. Do you think I was overthinking her actions or do you genuinely think she befriended my husbands ex out of spite?