Is my girlfriend's twin jealous?

To summarise as briefly as possible, I had a fling with a girl a few years back, we were really close friends for a while after.

Her twin then asked me out and we have been together ever since. But for a while after getting together the fling twin kept suggesting us breaking up and saying things like "well I slept with him first!"

Even before getting together there were questionable actions by the fling twin. Like trying to facetime me then saying she's glad I didn't answer as she was in the bath. And intending to apparently send a sexy pic to her friend to show to her at the time boyfriend, but instead accidentally sent it to a group chat of the friend and me.

Even more recently, considering the fling twin is infamous for never getting involved in pool parties. She came over for a party at ours in an over the top swimsuit to go in the pool with us, and kept asking why I wasn't taking my shirt off.

As it stands now we had an argument and aren't on good terms but I'm confused by it all. She told me previously she gets confused when we talk and get along like friends. So I'm not sure if she's getting in arguments because she doesn't like me or is clutching at straws for excuses to stop herself getting close to me.

At the same time there was a solid couple of years that I fancied the pants off her and other than that short fling (in which she told me she was sexually but not emotionally attracted to me), she spent the rest of that time pushing me aside to prioritize other guys.

I guess bottom line is im confused by her actions, we get along great and gave good banter when she allows it but she shuts that down and tries to start arguments a lot. I'm not sure whether that is her way of stopping her feelings for me or if she is putting on an act to be polite but genuinely dislikes me.
And whether she ever was jealous of the current situation or whether I just wanted her to be.
Is my girlfriend's twin jealous?
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