I'd say well if she's just some random woman would you mind deleting her
He can have who he likes as a friend. Asking him to change this is getting controlling.
OP, there's no right or wrong to being upset. The healthy set up is that it doesn't matter what you're upset about; your partner will respect your feelings, and you need to present them respectfully.
So, if you have an issue with your partner eating strawberry yoghurts, you don't say 'Could you stop eating strawberry yoghurts?', you say 'When you eat strawberry yoghurts, I feel uncomfortable/unsettled/upset/anxious/whatever'. In a healthy relationship, your partner won't want you to feel bad, and will prioritise that over the desire to eat strawberry yoghurts in front of you. They'd say something like 'Oh, sorry, I didn't realise that bothered you. Do you feel bad when I eat them at all, or just when you're there?' and then the conversation is open to find a compromise. In an unhealthy relationship, your partner will say something like 'What's wrong with you? Everybody eats strawberry yoghurts! Get a grip!'
If your partner prioritises having this woman, who is a complete stranger, as a friend on social media, over your happiness, he's not prioritising your happiness very highly, is he. No worthy partner would call you stupid for having your feelings, and no partner would get away with it, if you respected your feelings yourself.
You are allowed to feel anything at all, no matter how outlandish it might seem. Your partner should be interested most in respecting your feelings; they are a direct representation of who you are, and what your heart is feeling. Disrespect of that is disrespect of you at the deepest level.