Wow, very complex emotionally charged environment you are in. The girl may be flirting with other men because she has fears about you cheating on her and subconsciously wants to remind you that she is a catch, and that if you don't go for her others will. Sometimes when girls feel insecure they flirt with other men, it's an extroverted response to an internal problem. Some women who do this respond well to a take charge approach, when she begins with other men just go over take her hand and bring her closer to you / away from him, begin dancing and toughing her. See if she responds. For a long term solution, you need to sit her down and have a heart to heart, tell her that you want to settle down with her but can't take that kind of behavior. If she doesn't stop, she may not be right for you.
When you asked her how she felt about you she answered "I miss my ex's family"? That could be a sign that she was just thinking about him a lot at the time you asked and was feeling loss and remorse, which passes. Or it could be taken that she is not really ready for a new relationship right now. 7 yrs is a long time, because they lived together it was more like a marriage emotionally, and those bonds are hard to break. I will lovingly worn you that people who go through divorce and get into a new relationship right away often "cheat" with their ex's, this is because of those hard to break bonds, people feel closed to their ex's and express this caring/love the way they used to - sexually. Not all people cheat in this way after a long-term relationship breaks up, but some do. Why did they break up? How long ago was it?
As for the friends not liking you, sometimes this can be resolved by being loving, open, and attentive/responsive to them. Sit down with them express how much you care about this girl, ask their advise on how to make her happy or care for her in some way/ meet her needs. Emotional connections really effect women's opinions. This will help to turn around their view of you. Right now you are the new guy who is a possible threat to the stability of their relationship with her, and they are also unsure of your intentions with her. Connecting to them and expressing how you know, how important they are to her, may help with this.