Ok so I have been dating this girl for 3 weeks. We have tons of sex, she is insatiable. I am a lot older than she is. I'll be 40 in a couple of months and she is 23. So we were fooling around on the sofa and we started watching some porn (her idea). She shows me all her favorite videos. It was all MFF threesomes and lesbian porn. So she tells me she fantasizes about a 3some but she has never been with another girl. She also mentioned that she is afraid she would get jealous of another woman having sex with me. So how do I make comfortable with it? How do I make this happen?