Hi there,
From what you have told me, and from my own experience, I believe that what those girls are doing to you, is just flirtatious behaviour that makes them feel better about themselves and also send a confusing message that they are interested in you in some type of way but they themselves are not sure about it.
It could also be the case that many girls nowadays identify as bisexuals so even though they are in a opposite-sex relationship, they might think they are missing on a same-sex relationship (whatever type), thus sending mix signals (assuming that you are a girl interested in girls).
I do not think it is jealousy, it is just increasing one's self-esteem and confidence of being able to get whoever they like, whether that is for a short-term or long-term thing, and whether it is for a one-time or continuous occasion. I know a lot of people from my university that have done that to me and I am pretty sure that I have done that to others as well, probably both intentionally and accidentally.
I hope that my personal view on this helps. Hopefully others will be able to share their perspectives as well.
Best wishes.