M18 w/ F18
So it appears I have this peculiar defence mechanism where if I feel upset about myself in the relationship I want to cut her off, break up and leave forever.

I am quite possessive/ clingy, but I only happen to think it but not show it. I want to be around her all the time, want her to do stuff with me and I feel extremely anxious if we cannot see each other for brief periods of time.
I have the ambivalent-anxious attachment style to the bone, and it turns out no amount of love from her soothes my feelings.

She went away for like 14 days which put me into an awful state of mind and I of course immediately started thinking that 'she is not right for me' and that we should break up. I have an edge in finding reasons to why I should do that, so naturally the rationalization was on point. I slide into narcissistic thoughts about how better I am, and how I would be better off with someone else.

I figured I might be scared of abandonment and reject her to feel like I am the one in power in this situation. The abandonment theory is proven by the fact I can never actually break up, nor give a slightest clue about me having such intentions. I also noticed I would get extremely anxious if she doesn't like something about me and there is a possibility she would leave.  However, it doesn't happpen a lot.

On the surface, everything in our relationship remains perfect. Nobody would have a slightest clue that our relationship isn't working. Every thought I wrote about here is only manifesting itself inside my head.

I am a 2-year attendee at a councellor's. I also started taking antidepressants just a few days ago. Despite this, I still find your contributions very insightful :)