I need help. I did something admittedly stupid that made my gf break-up with me.

First, just to clarify, I didn't cheat or anything like that.

My gf and I have had some trust issues for a while. Specifically she had trouble trusting me (there were reasons for this, and I don't completely blame her). We have been working through them for some time. She had a very difficult time with the fact that I went to a very good friend's bachelor party a while back. We talked about it and worked through that. Things have been wonderful since. We went and had a nice evening tonight - a couple drinks and dinner. During dinner, she was opening her heart and pouring out her feelings, saying how her trust was returning, and she loves me, etc... it was very sweet. My eyes were getting teary. She mentioned the bachelor party, and how things have been going pretty well...

Now the kicker. I have been invited to another bachelor party, and totally forgot to tell her about it. I didn't RSVP yet. As a matter of fact, I sent a tentative email telling him not to plan on me, but will let him know ASAP if things change. I VERY STUPIDLY told her this in the middle of this deep open conversation we were having. Smooth.

I really do have a tendency to forget things, always have. Sometimes even kind of big things (never her birthday or anything like that).

Now that I wrote this, it sounds really stupid and trivial. But I actually do understand where she it coming from, given our history. I am VERY upset that I did this. I really want this to work. She is wonderful, and has made me a better person.

Thoughts? - What do I do?