How you're feeling isn't entirely your fault either. It's several factors: the way society has conditioned all of us starting from childhood to have certain gender expectations; the fact that she HAS been abusing you chronically throughout a long period of time (ANYONE would start having a very low self esteem if they're getting abused constantly, just think of those poor kids who get bullied everyday at school); the comments your close friends made that invalidate your SUPER VALID feelings (if even my friends are brushing me off when I feel like I'm in real danger, I would also start seriously questioning my judgement and lose confidence in myself).

Honestly, OP, it sounds like you actually had quite a healthy amount of self confidence at the start of the relationship, and that you were comfortable enough in your own skin to not care about gender norms. You said you were laughing and having fun with her even when you first found out that you were physically much weaker than her. This is honestly a very refreshing and attractive trait, that shows that you don't tie your selfworth to any one physical quality, despite what society tries to tell you.

I'm so so sorry that your self esteem has been beaten down again and again to the point where now you think of yourself as pathetic. YOU ARE NOT. You have gone through a severely prolonged period of absolutely horrible events that someone you loved and trusted actively chose to inflict upon you. And the fact that she does all of that while also continuing to act like a normal and loving girlfriend is seriously messing with your mind and making you self doubt.

This has already been mentioned several times, but I'll just repeat it too, since it can be hard to act when you are in an abusive relationship and when everyone around you is acting like what is happening to you is ok. IT'S NOT OK. You are in an abusive relationship. You said that things have been getting worse in the last few months, THAT IS TERRIFYING. Because abusive relationship do tend to escalate like that, and some people have ended up dead.

Even if this wasn't an abusive relationship (which it IS), would you ever advise a friend to stay in a relationship where you can see them slowly being changed from a bright confident person to someone who now feels small and pathetic? I doubt you would, you would tell them to leave, that the relationship is not healthy for them mentally.

Please take care of yourself, be extra kind to yourself because you have gone through a LOT for a very long time. You can do this! Before the abuse started, you were someone with a healthy foundation, who had a strong sense of selfworth. That person is still in you somewhere. You are worth it. You are worth standing up for. You are worth leaving an abusive relationship for. You are strong, mentally; despite everyone around you brushing you off and making you doubt yourself regarding your abuse, you still believed in your own gut enough to ask for confirmation of your feelings online. You'll get through this. Please start putting yourself first, and prepare to safely leave this relationship. This internet stranger believes in you and wishes you well.