Hi I wanted to post this as there was no reply button to your post. I really feel for you, I am a full time working mum, I started back at work when my DD was only six months old. I admit she was staying with my mum so I was alot more relaxed than having her in day care. I don't think there is a right or wrong age to start leaving your child alone with somebody, you ahve to do what you think is right and you will be amazed at how the behave when your not around. My daughter is at the point where she would prefer to be at her nana's than at home. More exciting!!!
If you can find somebody that you trust with your son you will find it very rewarding. It's the first step that is the hardest but you will both get used to it and he will probly love being babysat every now and again...It must be hard not having family around to help but maybe you could advertise for babysitter and get to know them before you leave your son in their care, invite them over while you are there and let your son get get to know them and see what happens. You will feel alot more relaxed as you have gotten to know them aswell. hope you get your well deserved night out!! good luck! What area are you from?