I got married when I was 21...when I was 23 my husband cheated & left me for his pregnant girlfriend....just called one day and said he wasn't coming home again. I was devistated for years - I DID NOT BELIEVE IN DIVORCE and was horrified that I was now that statistic. I felt like EVERYONE should make EVERY EFFORT to make a relationship work. But you know what? He was miserable, and I was miserable.
Now, over a decade later, I have the most wonderful husband and son I could ever ask for...and my ex married the girl he got pregnant, they are still together and have 2 children.
It's tough, and your opinion of marriage/children is what is going to make the difference, but I have to say I am (now) a believer that you do only go around once and it's not good for anyone in that home to be unhappy. If you do have a child/children, you either have to make efforts EVERYDAY to make that home a happier one or you need to make that tough decision to move on. I can't imagine raising a child on my own and give all the kudos in the world to those who can. You really have to evaluate what you are capable of handling if you leave, but I am also a firm believer that God only gives us what we can handle.
Best of luck to you. I hate to see you call it quits, but if you both could move on to happy relationships with someone else (even if it's a decade later like it was for me), it's better than a household of sadness.