Stop feeling badly! You are doing exactly the right thing! He's safe and I assume the apartment is childproofed, right? Outlet and cabinets are secured, venetian blind cords are up high, and so on?
Children LEARN through playing and exploring on their own. So constantly entertaining them is actually damaging. If moms (or dads) are with their kids every second, the kids never learn to be independent, they never manage to go to school and separate from parents, they never develop a sense of self. They also become very demanding! They absolutely MUST learn that you are a person, that the world does not revolve around them, that other people matter. You can (and should) clean the kitchen,fold laundry, go to the bathroom, brush your teeth, and go on the computer. You can hear him playing, so you know that he's not hurt or unconscious! So he's fine.
And don't feel that toys are the only things he must have. Let him play with pots and pans, tupperware, funnels, wooden spoons, and so on. Put a plastic colander and a pitcher in the bathtub, let him stack tupperware containers, let him pick up leaves or pine cones (not the super sticky ones, for your own sake!), maybe put a little bird feeder on the outside of the window (the kind with suction cups), give him the cardboard roll left after paper towels or toilet paper are gone (show him how to make sounds by talking into it), put stuff in an empty carton, and so on. There are all kinds of things that can be fun - textures, colors, shapes! It's about the variety of experiences, not the sheer quantity. Also, put some of his toys in a box or bin and put it in the closet - rotate those toys out periodically and put others in their place. Everything seems new when it's been gone for a week!
I do think taking a parenting class or getting into a mothers' group would be great for you. I found a weekly play group through our local Newcomers' Club, but the library often has something connected with a story hour, sometimes the Y or a church or a synagogue has something, and more. Get connected with resources in your area. You'll make friends, you'll get support and handy tips, and you'll learn ways to deal with different personality traits and phases.
There's a wide range of what it means to be a good parent - and there are stages of child development that are easy to learn without you feeling that you have to be a child psychologist. But remember that lots of people have different opinions, and they aren't all right - or they may be right for THEIR life and THEIR child, but not yours. We all parent based on how we were raised (keeping the good, getting rid of the bad), and we all see things in others' kids that we either admire or abhor. The point is not to work in extremes, and not to be so hard on ourselves. Your child, and mine, didn't come with a manual!
And remember that every child gets hurt, many children break a bone, and most parents lose their tempers or feel stressed. These are not measures of good parenting.