Oh good, do try to relax (I know this is easier said than done). I would try the following:
Leave food out around the house for him to help himself to, and don't comment if he eats it or if he doesn't eat it. A little plate with lots of attractive finger foods on it is appealing for this age group - you could try pitta bread sliced up, tiny tomatoes, raisins, green and white grapes, cubes of cheese, oatcakes spread with something yummy, little bowls of dip (hummus, sour cream) etc etc. Just put it on a low table near to where he is playing and let him help himself if he is hungry. Don't make any fuss about it or keep mentioning it, or make him sit down and stop what he is doing or anything. Good table manners can come later.
At meal times sit down and share the same food together. Again don't comment if he does or doesn't want to eat. Just try to make meal time fun and happy. You could put a nice CD on or play a game together while you eat such as I Spy (don't bother with the letter thing, just ask him to guess what you are looking at)
I would also try to get him involved in choosing and preparing food. Go to a market or greengrocers (much more interesting and friendly for children than a supermarket) and talk to him about all the different fruits and vegetables. Let him run around and touch the food (just check you pick a shop with friendly staff in first - you could even go in alone and ask for their help with this, get them to make a fuss of him etc!) Let him choose some of what you are going to buy and then let him try something he has eaten straight away (grapes seem really popular with this age group).
At home let him help wash and prepare the vegetables (mushrooms are great to chop with a blunt knife). Make cakes and bread together and eat them warm from the oven, let him mix his own cereal from different packets and pour in the milk himself. Go to a Pick your Own farm, or visit a friend with an allotment. Let him see the food growing, and let him pick it and eat it right there and then. It tastes so good and is exciting for a child. You could also try growing some food yourselves if you have room in the garden, or even just herbs or cress on a windowsill.
Giving him back control over what he is eating is important, and what you want to aim for is letting him take charge of what he eats and when. He should not be eating because you want him to, but because he feels hungry and knows that when you feel hungry, you eat as much as you need (or as little as you need) to feel satisfied. I would only have food in the house that you are happy with him eating, and then give him free rein. It doesn't especially matter what or when he is eating, try to make food a fun and sociable activity once more and not a big stressful issue. I do hope any of these ideas are useful to you.