I've been in a relationship with my boyfriend for almost a year and a half now, but I've had this consistent anxiety about his ex cropping up throughout the relationship and it's depressing and stressing me out! 

He was in a FWB relationship with this girl he worked with for about 3 months until she had to up and leave the country. She works as a model and it's clear why. He developed feelings for her but the feelings weren't mutual. She left and continued to send him nudes and sext him until she cut contact with him suddenly. He was so hurt by this and he struggled with the fact that his feelings weren't reciprocal. We got together 2 months after she cut contact with him and it was pretty clear that he was still not entirely over it all, despite claiming to be. 

She had no contact with him until October last year (after 4 months of radio silence)) when she messaged him asking him if he could pay for her plane ticket back home cos she was in trouble. Apparently he was the only person who could do this for her. He only told me about it whenever I found out she was home, which stressed me out and didn't help with my fears about her ruining our relationship. Once she was back in the country, she promptly ghosted him again and hasn't been in touch since. 

Now, he tells me he is over her, but only recently has he been able to listen to songs that remind him of her, and he brings her up and looks at her Facebook every once and a while out of curiosity which terrifies me. I am frequently finding myself shit scared of him not being over her and getting in contact with her. I have a seriously hard time with the idea of her and it puts pressure on our relationship. He loves me dearly, it's clear as day, but my obsession and paranoia about him not being over her takes its toll on us. 

She is this gorgeous model, tall, skinny, perfect skin and hair, who is confident, doesn't give a shit what people think of her, and is mentally stable. I, on the other hand, am living with BPD, frequently having 'downers' and doubts about the relationship, average height, chubby, pale as death, average looking, timid and haven't enough confidence to even fill the top of my little finger. How the hell can I compete with her? 

People tell me "She's his past. He's with you now" which doesn't really help me because my argument against that is "Well he's with me because he didn't have a choice with her. He wanted her love, she only wanted sex. If she wanted him back, he wouldn't be with me"

Ugh, I don't know how to cope. It makes me so self conscious and I hate her. I wish she didn't exist, and I'm terrified of her contacting him again and him developing feelings again. How do I cope with this insecurity and fear?