I completely understand what you mean! It can be so tricky to meet new people and feel like you have to be 'on' all the time! Am I right in understanding that you feel like the person closest to you is talking about things you feel like you can't relate to? If so, I am wondering - could you express how you're feeling to this person?
I think I have to agree with what @Lost_Space_Explorer5 and @Anonymous have said, I think this is something every single person feels to a degree but we are only just beginning to create safe spaces to get real about it! I was wondering if you are able to chat with you gf about this at all? She might be able to provide a bit of extra support?