"You will never be able to mother him into never feel sad or insecure."
Agreed, merrymouse. You're getting some great advice from all quarters here, turtle, imo.
One of the central tenets of attachment theory according to Winnicott, a psychoanalyst who worked widely with infants and the parent-child relationship, is that of being the "good enough" parent. A significant part of this is to be able to contain a child's otherwise hard-to-bear feelings; in other words, you, as the parent, are able to demonstrate to them that difficult emotions can be survived.
"Survive" sounds like extreme language, but in the eyes of a small child who depends completely on others for its survival, anything that is unpredictable or which causes distress can feel like that kind of a threat to its survival because it shakes the foundations of their world.
The point is that we cannot avoid these threats -- many of which are things we'd consider 'normal' such as an infant's realisation when it wakes up that 'mother' is not in the room. To that infant, in that moment, she has ceased to exist. The point is how the parent reacts to these threats. Is s/he attuned to her/his child's needs? Can s/he hold and soothe that child when they are expressing distress? And, in this case, can s/he demonstrate that s/he is able to withstand and bear the child's otherwise unbearable emotions for them?
Which is why your ability to look at, sit with, bear and process your own emotions is essential.