Why is she texting my fiancee?

Betty says:
So I've been engaged to my fiance for about 7 months now and known him for 2 years. We have a lot of mutual friends. We have a couple that we're friends with that are from my fiance's best friend's side. They are about our age (we're all in mid 20s)They've been together since high school and married for over a year and a half now. We all hang out in a group, its fun. The girl and me have become pretty close and I like her company. We even went on vacations together. We'd text here and there to catch up or to invite one anoter places to hang out all together. The thing is I noticed this girl has been texting my fiance now instead of me. When her and her husband are supposed to come over, or were meeting them somewhere, she calls Him and not me. I'm not the type of girl to get jealous over little things, but that got me thinking. Is that weird? I can't recall anything happening between us two, she's always nice. Even my fiance thinks its weird. They knew each other before me, but really? 

You're not imagining it - clearly this girl is attracted to your fiancee. It is tempting in these situations to believe you're overreacting and there's nothing to worry about. My wife in your situation would be decisive - she would drop this couple like a stone! You do not need to confront them - only your fiancee. If he loves you he will respect your feelings. Simply stop inviting them or accepting invitations. If they confront you, you can either be honest about how you feel or be evasive - that's up to you. But I have no doubt that if you just let it ride things will end badly.