Hi aanaph
I see that this is your first post, so...

Glad u found us here at PC!
I'm sorry to hear that you are in such distress at but, I am very happy that you are,able to write this bc it shows great strength, humbleness, openness, and desire to change, to not only be able to pinpoint the behaviour that is bothering you but also owning it This is a very difficult step for many to take...so Congratulations! You have taken ur first step towards healthy change .....and that makes you mighty!
I am not a dr, therapist or any sort of MH professional, so I am not in any way able to speculate what exactly may be the causation or correct diagnosis that can tell you why you do this....all I can offer is general information, advice, and support from my own personal experiences, interpretation of others research, and POV. Please take it or leave it as just that
Generally speaking, to my understanding, mimicry or taking on/ mirroring aspects of those around us is something that we all do at times to a certain extent...bc mimicry is probably the earliest and most deeply ingrained way that we learn about the world and our place in it from infancy..actually in utero as well...now as we grow we start to "take some and leave the rest" and begin to form our own independent solidified identities....but when, for many possible reasons, we somehow do not develop our own individual identity...we can become "stuck" and /or confused. We do not know what we are lacking or who we are supposed to be....this developmental stall creates n identity disturbance. Identity Disturbances can present in many ways and if not addressed early on...tend to result in all sorts of "maladaptive behaviors"...we may not view them as such bc either they don't cause us distress and or they are the only way we know and we sometimes can figure out how to make them work in our favour. Many MH disorders may include soe form of Identity Disturbance...Mood Ds, PDs, DDs, and Trauma related disorders....also mimicry is common in social anxiety and other self esteem issues....so yeah, pretty much across the MH spectrum they can occur... I would talk to your psych team or show them this post next app you have...they are best suited to understand what the most likely causes your particular presentation may be. Hope that this is helpful as a starting point for you, sorry I can offer you anything more specific...but, I suggest writing or pasting this post in the New Members forum...that way more members may see it and possibly some can relate more to their own behaviors and can offer better perspective.
Hope you find much comfort, acceptance, and wise words of wisdom here,at PC! Be Well and KEEP WRITING!