Next door neighbor

I need advice and I’m getting to the point where I do not know who to talk to about this.

Anytime I even try to talk to anyone I feel like no understands or doesn’t give me the best advice and I just don’t know what to even say or think at the moment. Or even what to do.

So my fiancé and I and our 4 kids moved into our new home in July. Our neighbors are a man and woman with two kids we thought at the time they were married because that is what the neighbor lady told my fiancés mother. But from my research they are only engaged anywho back to the story. So since we’ve moved in I haven’t really spoken to the neighbors much because I just keep to myself and my family. Well my fiancé on the other hand very social so he started communicating with the neighbor fiancé a lot. They’ve even gone fishing a few times. And he also communicates with the girlfriend a lot. And to me at the time I didn’t mind because that’s just him well things started getting really weird to me. Every time I would go outside with my children or for anything at the the girlfriend literally never speaks to she doesn’t even say hi to me to be polite well I started to think to myself that just weird she would always talk to my fiancé any chance she could literally he would come home from work and I would find her coming out just because she knew he was coming home work and she would make conversation every single time she would keep doing it more and more even if he was doing some yard work she talk to him. I noticed previously on the 4th of July she tried sneaking off with my fiancé to look for sticks for s’mores in the dark at time I didn’t really think anything of it and I remember blankly she that night her boyfriend tried to kiss and she wouldn’t. Well recently we were outside cooking out as a family and I really didn’t want to because of her I was starting to catch on what she was doing but I did anyways well we cooked our food and decided to come inside to eat as soon as I came inside she noticed he was still out there and I was not and she started talking to him again! Just because she knew I was not out there! I got upset and told him I’m no longer hungry you can go continue to talk to her cause I felt sick and I was catching on and she didn’t even care she just kept doing it. Her boyfriend not once tried to be disrespectful in that way ever! Now and I being crazy or is she trying to get with my fiancé in some way!? My fiancé tells me I’m being crazy and my sisters and friends tell me she is definitely trying to get with him and that I shouldn’t worry because she’s ugly or whatever else. I don’t know what to do or think anymore. Now let me just say him and are not perfect in way we’re always arguing. And have our problems. But this is on another level of wtf?