Feeling possible symptoms of childhood trauma yet only remember one possible causal event?

Hello.

I have lately, through a period of increased introspection and care for myself, begun to get a better view of my psyche and my almost perpetual sense of anxiety, especially in relationships. I am currently in a relationship with a woman who is so understanding and lovely and emotionally intelligent that it genuinely stumps me over and over again. In spite of this, I still feel and overwhelming sense of anxiety concerning our relationship. I fear losing her, I fear losing myself, I fear what the world thinks of us, I fear my own psychic constitution as it relates to her. I also have the sort of abstract notion, noticed both in thought and (I think) in dreams, that she will suddenly turn against me and hurt me, which leads to a fear of any change, which is very hurtful both for me and for her as my fear expresses itself as both increased anxiety concerning her opinion of me and increased anxiety concerning losing myself which leads to avoidance, mostly subconcious.

My parents where always very good to me and verbally and in action loving, almost extraordinarily so. The only event I can at all recall that might have something to do with this is one from somewhere around my sixth year when I slept over at my grandmothers apartment without my mother or father. Sometime in the evening my grandmother, who had been an alcoholic around 15 years before but who had since then not touched the stuff, took some sort of drug pill which made her change the way she acted. I do not remember much of the evening but I do remember being completely terrified and sitting in the corner of the room crying. I don't think she was directly mean or inappropriate to me during the night, all I remember is her eating ice cream out of a milk carton somehow and that that imagery was terrifying to me. I think it terrified me the way she changed so suddenly into someone else and that I had noone else to help me or take care of me. My mother came and picked me up in the morning and was angry at my grandmother like I have never seen her angry before but we have since then reconciled and now have a very good and loving relationship.

Can one event like this leave scars like those? How can I help myself through this so as to not hurt myself or others any more?

Thank you for reading, and please write if you have any advice or thoughts at all. English is not my first language, if anything is grammatically weird.

-Theo