Holding Everything In Hurts

This isn’t a physical hurt, it’s more like I can feel my mental capacity cracking like a thin sheet of ice. It wasn’t anything sturdy in the first place, years and years of knock backs have been wearing my mental strength thinner and thinner.
It’s a very delicate thing and it’s cracking. It’s my fault it’s cracking because I store resentment, I hold on to it like a sponge. Small things that make me unhappy, small things that people have done that have upset me I will store and keep until I crack.
Like when a dam is holding back too much water. It will hold it back until it can no longer hold the pressure and it breaks. I’m worried that is what’s going to happen to me and then what? Will I just be a shell of a person?
I know what’s caused it, most of it is lots of tiny things that continue to build up and then there’s the one main cause … there’s him. If he had any idea of how much he’d hurt me, if he even knew about the panic attacks I’ve had in my room, the fear I’ve had about leaving the safety of this house out of the fear of seeing him with her. If only he knew how small and insignificant he had made me feel.

I just want to crack and let all of this out, but I’m worried I will take it out on the people I care about most so I need to keep all of this building up anger deep inside so I don’t upset anyone around me.

Even if I do decide to try and figure this out I’m not sure how relevant everything that pours out of me will be.
I’ve tried talking to people about how I feel before and it just doesn’t work. I can’t do it. I’m not an open book, I don’t vent to people because I don’t like letting people in. I don’t want others knowing that some people have such an ability to impact my life so much.

I don’t like showing weakness, so although holding all this hurt in is bad, it would never be as bad as showing weakness.