Feeling jealous over my wife?

I have been happily married for 12 years iam 40 and my wife is 34 , she is very pretty when we met she lived with very overprotective parents and even at 21 had to be in at 10pm , needless to say I was her first b/f , a mutual friend got us together , I soon began to notice she used to get very giddy if she used to see good looking black men , and I felt a bit embarrased as I felt it undermined me but I used to let it go , but although I trusted her and still do it did make me think that because I was fair that I was not really her type and that she got with me because I was the first attractive person she had dated , however her head continued to be on a swivel and I started to boil over a little which drove me to finish with her but she was devastated and that kind of made me feel more secure so we got back together , she did always say that she was never looking I said ok but never believed her but put it all behind us , however she has just recently started the same patten again over the past 3 months I seen about 6 black guys smiling back at her , she says tat she is a people watcher and looks at everyone and that sometimes her smiley nature gets reciperacated but I have never seen her look at anyone who is similar to myself and with the demise of our love life past 12 months just wonder if she has lost all attraction i have spoke about it and she does love me dearly and very doting but iam little confused is her behaviour flirting?