The background: My dh has had a good friend, who is a girl, for around 12 years (we've been together for 4). For most of that time they've been 'just good friends', apart from a short period of time when they slept together two or three times (I think it went on for a couple of weeks and my dh was depressed at the time). He told me he felt sick after each time they did it - that it was like sleeping with his sister. He went away travelling and when he came back, they must have somehow decided they could only be friends, as he didn't feel 'that way' about her, though I know she felt strongly for him. Since then, she has had one or two serious boyfriends and is currently with one who she is desperate to marry. She and my dh still see each other once every two months or so, and I see her too - with or without my dh.
My problem is I still wonder if there is anything simmering underneath (on her side; I definitely don't think there is on his). She is lovely about me and our marriage and our dd, and she is v happy with her boyf, but I recently found a fairly intimate card she had sent to my dh years ago, which he has kept alongside b'day cards etc. from previous girlfriends. I know there's nothing going on but I just can't help feeling jealous. What's wrong with me and how can I stop?!