First of all, if your family is watching 3 boys when you work and or go to school they ARE helping a TON! The cost of putting 3 boys in daycare would be staggering. I'm a little curious about your situation. It's hard to know what to think for sure. But since you say you leave them with family for work and school, I assume you don't have daycare and you probably don't pay your family. Maybe they are not really meaning to call you a neglectful parent. Maybe they are responding to being used for daycare and not getting paid for it. Three kids would be a major handfull for anyone to take care of and if they are doing it for free they should be nominated for sainthood.
About their dad. Why isn't he helping? If he is disabled you can get social security. If not you need to be working with child support enforcement to get financial help from him.
As far as dealing with stress goes.. You can meditate. If you have cable there is some great music channels with relaxing music. If not, got to the library. I bet you can check out some relaxation type cd's from there. If you choose to meditate, make the boys lay down and do it with you. I do this with daycare kids in the house and use it as the way to get them to settle down for a quiet/nap time. They don't have to sleep, but they have to give me a break when I need it. You don't need to be away from your kids to get some relief. You just need to change things where you are.
Outside of this, you probably need to spend some time forcing yourself to think positive. Make a list of all the things you can be thankful for. Count your blessings. You do have your hands full. This time in your life will pass.
Suzi