Hey dude. Sounds like a tough situation you're in. Ive been in a similar situation myself and so I will try to help with some discussion/advice.
Being broken up with is hard. But time is always a great healer. It won't hurt like this forever. In 6 months time it will feel very different to how it does now and then again 6 months further down the line. For me I spent about 6 months missing the feeling of her being around and wishing she would come back. Then there was some cold realisation that it's not coming back and that my life will never be the same. I had to come up with a personal motto: DTAH (don't think about her) just to stop my brain from dwelling on it.
My job was similar to yours but it came later. About 2-3 years after the break up. So, a different experience to what you are going through. However it underpaid like crazy and consisted of a really tight knit "family" of people who all looked out for each other.
It sounds to me like you would probably benefit from.staying at your job for a while, perhaps another year? When you are feeling a bit more comfortable, see what you can do regarding a raise - explaining that you are feeling very undervalued. If they do not give you a significant raise then you do owe it to yourself to move on once you are in the right place emotionally. And that will come.
Are there any hobbies you could see yourself doing now with your free time? When I started my job I spent all of my first paycheck on a fancy mountain bike and got really into that. It helped provide a good balance of something healthy, vaguely productive and challenging that I could do outside work so that work wasn't the only thing going for me. I didnt use it to make friends, at first, but eventually it made friends for me (albeit not close ones) because I got good at it. Mountain biking was an awesome outlet for me and I became one of those people who was happy to work a slightly unfulfilling job, provided that it gave me enough disposable cash to pursue my hobby.
I broke my collar bone doing it last year, which changed things a lot. But don't let that put you off if you're considering that particular sport, it only happened because I was getting very ambitious and was doing it an awful lot. When I broke my collar bone it gave me 6 weeks off work, and a lot of time to think. By this point I had completely gotten over my ex and was now just happy to live my life for myself. I realised that although the friends at my job were awesome, that I deserved better and owed it to myself to do better, and something that I actually wanted to do as a career. I quit my job and am pursuing a career as a doctor now. It has been difficult and risky but I know its right for me.