Im a young girl, caught in the crossfire with co-worker?

[shelburnect3]

I started a new job at a horse farm about 6 months ago. There are only a couple of us that work there. I am 20 years old and there is guy that that is 26, who works with me. His name is Wes. I kind of have a crush on him. He's not exactly the best guy for a girl, but he does have a good heart and he is always nothing but nice to me, despite his past.
His girlfriend named D, is 25 years old. She has 6 kids, none of them are his. Shes not really attractive in the least bit, dyed red hair, beer gut, foul mouth, etc. Apparently she's bi-polar, has trust issues. She and Wes have been together for almost 5 years. During the five years she's had 2 children with another guy, while they were taking a break/off and on. They fight just about day in front of everyone at work. He always starts drinking before she comes.
After work is done, D comes to pick up Wes and drive him home. Before you judge, they live in a rural area and it is not uncommon for one family to share a car, phone, etc. D is polite to me and always say hello when she sees me.
The other day I had went down to the farm to take photos of horses for a project. Wes was there by himself finishing work. I had my older cousin, 24, and her daughter, 3, with me. I offered him a ride to the store, in case he needed anything. He agreed and we drove to a shopping plaza and he went inside a grocery store and cousins and I got McDonalds.
When I was dropping him off at his house, he said "I really enjoy yalls company and if you guys want to kick it, that's fine". so, I asked him if the baby could sit down and eat instead of eating mcdonalds in my car. We went inside to his kitchen and sat around a table eating. His mom was there cleaning. He brought out some baby pictures, while his mom decided to tell stories about him. His mother really likes me. About 10 mintues into eating he looks at me and says "You know who is going to be coming by any day now." and I say to him "Who?", and he makes a face and says "she's crazy". Low and behold, ten minutes later she pulls up in the driveway. He goes outside to greet her. 3 minutes later she comes inside and her face is beet red and she mouths the words "hi" to me and does a half smile. I say hello and then she turns around and walks out the door. She looked like she was on the verge of crying or already was. They usually go for car rides while they fight so, after she left they disspeared for 15 mintues and me and my cousin decided to leave while they were gone. I didnt think anything of it until I was on facebook and looking through wes' page and ran across hers. She posted this: "PLEASE HELP MY FACEBOOK FAMILY: yesterday my boyfriend of 4 years knew I was on the way over. I pull into the driveway, he comes outside and says ‘dont get made but there are 2 girls and a baby in the kitchen and you know one of them, it’s (my name).” ok, i have been told that they were already talking and i told Wes that i didnt like it. he didnt CARE, HE DOES NOT CARE, I DONT KNOW IF THEY WERE TALKING BUT I DONT KNOW WHAT TO DO...........” everyone that commented on it said to leave him. She posted this at 3:20 in the morning.
When me and my cousin got in the car, she told me that D feels threatened that a younger, pretty girl like me with no children is friends with him. I do agree but my personality and demeanor is not tempting for a guy. I am a virgin, in school for photography and dental assisting, work, etc, not that much experience with guys. Me and D are polar opposites. What do you think of this situation and is it really that bad for guys with girlfriends to have female friends?
Was I in the wrong? He invited us inside and I accepted. How bad does 2 girls, a baby, and his mother cleaning look? And the part about us “talking” is untrue. I do not flirt with him nor call, text, when I’m working, I am working. me and him get along but I would not “talk” to him out of respect for her and I would not want anyone to do that to me. Now there has been mutiple times where Wes and D have gotten in fights and he would beat around the bush and ask me to hook up with him. Obviously since I am a virgin, I am not going to do that. HE did not know that until recently. When he found out he said "I was a good girl." and from then on, he's been really subtle with the things he does and says.
Im trying to figure out if her reaction is an over-reaction or guys are really supposed to be isolated from all other females... Any genuine advice is appreciated. Like I said, im not exactly the most experienced and shes a mother of 6 and they've been together off and on for 4 years.

[Wakeup]

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