You’re 28 and the two women in your life, your girlfriend and your ex-girlfriend are 28 and 23, but I’m not sure which is which. And… I’m not sure why you broke up with your ex-girlfriend two years ago — and that’s important to know. You said there were issues on her end — are they now resolved? Since you’re considering breaking up with your current girlfriend of a year to get back together with your ex-girlfriend, you should really focus on what broke you up and how things are different, so that if you do get together with her again, you won’t run into the same problems you once did. 😉 You said you’re terrified of having your heart broken again if you get back together — which indicates to me that those problems still exist and are unresolved 😳 I think that’s the beginning and the end of this. Unless you can really talk about how things are going to be different — rather than how petrified you are of them being the same, it’s not going to work.
As for your being sick about knowing your ex-girlfriend is with another man (even though you’re dating another woman), the best remedy for that is to accept the fact that the two of you have broken up and truly move on, without contact. That will make the break up complete. And… if you can’t do that, then maybe you’re not done and for better or for worse, you need to give it another try so you can find out one way or another if you can make things work with your ex.
There is no “romance insurance” so you may have a broken heart at the end, or you may have happiness and a long-term commitment — but if you don’t give it a try, you’ll never know. 😉