Is he cheating or at the very least? Is there something going on between them?

me and my boyfriend have been together four months. the other day I saw a girl that he was following on Instagram and when I questioned him on it, he said from work at first, and then said he doesn’t know her that he just followed her and that was it.

so me being nosy, I followed her she accepted mostly immediately and then a day later she had followed me back, and I added her to my close friends list on Instagram. I have a bunch of people on my close friends list on Instagram that I don’t know. I didn’t see a big deal for me. I’ve posted him and me in the past, and I took a screenshot of him telling me how much he loves me and posted on my story and immediately she saw it and then made a comment on her Instagram “you don’t even know me and I’m added to your close friends 😂” it was directed towards me, obviously, and not him but then quickly after she deleted it.

she must’ve said something to him because immediately he started flipping out and saying that “I’m weird” and “stupid” and how he wants nothing to do with me anymore that i need to disappear just super angry and accusing me of writing her when I didn’t write her until after he had said something because I was confused on what I did wrong because again, I’ve posted him before not thinking anything of it.

anyways, she had told me that there was nothing going on, and they never was that they’ve only known each other for “days” and to calm down and that I need to talk to him about this that she wants no part of this.
Is he cheating or at the very least? Is there something going on between them?
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