The pain you're going through now is from your girlfriend leaving, correct? Unfortunately there's no easy fix there, you just have to go through it. It's brutal (I went through a similar experience 4 years ago and couldn't see how the pain didn't kill me.) While this sounds cliché and it's incredibly hard to imagine, it will get better but it takes time. I was not walking with God and didn't lean on Him when I was going through it. I wish I had a better answer for you but it's something you just have to get through. Keep seeking God. I can't stress that enough.
You said you're having a hard time hearing God. I find when I can't hear Him usually one of two things is happening - either I didn't do the last thing He told me to or I'm not being still (something I struggle with!!) I'm guessing your mind is racing, replaying everything to figure out why she left. The reality of that is you may never know for sure. In reality, it doesn't matter why she did, it really won't change anything for you. Your challenge now is to move forward and for me, that was really overwhelming because just getting through each day was all I could do. But I did get through each and I did move forward. There's hope, I promise.
When you pray, tell God what your struggle is and ask Him for scripture. Countless times I've done this and He'd led me to scripture that was, of course, exactly what I needed.
Do you use the YouVersion Bible app? It has thousands of awesome Bible studies and I find those so helpful as well.
Pain go now in Jesus name. All emotional and physical pain go now in Jesus name. Be healed and whole, physically and emotionally in Jesus name.
I'm praying for you.