I believe an infant that is breastfed has a good chance of creating a stronger bond. That bond can lead to a child feeling secure and happy.
But it doesn't guarantee those things. Life experiences can alter feelings of security.
My youngest, the one who received the most breast milk for the longest period isn't a secure child. Social, yes but secure no. She is clingy, afraid of being alone and fears loosing us and her things. Living through and after Hurricane Katrina was a difficult experience for her.
That was just a personal example, of course. A child's parents divorcing, death of a loved one, abuse, lack of stability in the home are just some things that may toss the emotional benefits of breastfeeding right out the window.
All we can do for our children is give them our best efforts and hope for the rest.