Jealousy,Betrayal,Infatuation,… Or All these mixed up?

Im 35 and my friend is 33.Both of us are married with kids.He recently struck a friendship with a girl for physical benefit but withdrew and made it a normal friendship again as the girl was adamant that he shud marry her if he is looking for a physical relationship.Later he gave me this girl's number for me to contact her.I just started texting her and she too replied and we talked over the phone.Now my friend is jealous and upset whenever she calls me and he never talks about her whenever we meet.I told this to her and she told there's nothing wrong with him but still i feel that he is upset coz of me contacting her.Now the biggest problem is i too am jealous and upset whenever this girl texts or contacts him over the phone or meets him out. I don't know how to come out of this triangle but i feel that i've really made a good friendship with her without looking for physical benefit like my friend.Please reply me to come out of this web, but still i feel i can't forget this girl..