I'm sorry things have been so rough for you! But I'm glad you shared your story because you'll get a lot of great advice and support from the people on this board. Please know that you're not alone and, as everyone else has put it, things do get better.
I've also been dealing with anxiety (it started the year after I was diagnosed with IBS; I spent the last nine years trying to take care of it without drugs). I finally realized I couldn't do it on my own and have recently started taking an anti-anxiety medication and seeing a counselor. It's only been three weeks, but I've been noticing improvement.
How well does your girlfriend understand IBS and anxiety? Would it be possible for you to see a counselor together? Does she understand that you're suffering a lot more than she is? I'm sorry to bombard you with so many questions, and I don't want to sound harsh! I'm sure she's a good person because of how much you care about her. Maybe you should use this time apart from your girlfriend to focus on getting well. Or get her involved in your recovery. However, don't focus on getting better for her sake--do it so that you can live your life.