Stay in my marriage because it's what is "best for our son", or separate and be happy?

Long story short...or hopefully. I graduated college in May '04, met a guy that summer, moved in with him after 3 months, got married within 7 months because he was getting ready to be deployed again but it never happened. May of '07 we had a baby. Not "planned" but had been discussed that past year. We love our son immensely, sometimes I think he's the glue that keeps my husband and I together. Ever since I got pregnant, it seemed like things changed THAT second. Our relationship was pretty happy-go-lucky before but now we fight, disagree, avoid each other, blame each other, get jealous, and make snide comments at each other. All away from our son of course but I know he knows something is up. So now to my question: do we force ourselves to stay together or separate and see if we are happier? My husband doesn't work (on VA disability) and I have 3 jobs that help a little with bills. I won't get into to much detail about how I feel since my hubby can't defend himself. We tell each other that we "love" one another but it doesn't feel real. I have tons of faults that he always points out so I feel that if we lived in separate places, he wouldn't have to "put up with me".

It kind of feels like once I had my son, my husband checked out and now my son is taking his spot as the new "man" in my life. HELP!