I have a 5yr.old only child and sometimes it's so hard when they have noone to play with.
When my daughter was two she was in daycare which helped tremendously. Without daycare and me working I think we would have gone nuts.
If your a stay at home mom I would try and go somewhere everyday or everyother day. Go to a playgroup, library time, indoor playlot at the mall etc. Just keep busy, and socialize alot.
When you are home and have given your son alot of attention and need to get something done or just need some mom time let your son know. "Mommy has to pay bills, you will have to go do whatever and I will come play in 10min."
I tell my daughter every night when I'm on the computer or watching tv this is MY TIME, I'm a mom all day and I NEED my own time. She get's upset but it's to bad because this is the only time I get to myself a whopping 1/2 hour or whatever.
My daughter has nearly every toy she's ever wanted and is spoiled. She hardly touches her toys I learned that awhile ago there is no magic toy that keeps them busy for a long time.
I've learned to do alot of things with her side by side, I pay bills, she colors. I'm cooking she's helping with odds and ends in the kitchen. I'm watching tv , she's sitting next to me reading her books or watching with me. I'm folding laundry she's right there with me helping. The older my daughter gets the easier it is getting, she is pretty content as long as she is in the same room as I. If I'm on the computer in my bedroom she'll come in and sit on my bed with her toys for long periods of time and play but is content because I'm right there, if I get up she follows me like velcro. If I take a bath she begs to come in to and I tell her no I need to relax you can take your bath next and she'll find a activity to do sitting on the bathroom floor. I don't have any privacy but that beats trying to play 24/7 with a 5 yr. old. It's like we've neogotiated. We're also very busy on the go type of people and she loves that. I give her plenty of attention but have also put my foot down and shown her I need my own time too. We take alot of turns, she'll have to do something boring like going to a appointment I have but in return I'll take her to a chuckie cheese or McDonalds playland when were done. Were kinda like a team. It's just the two of us my daughter and I so we do alot of stuff together that we can both enjoy. I know it's harder when they're two but when they get older you can go to movies and out to dinner etc. and both enjoy doing the same activity. I just took my daughter to Buckhill to go snow tubing it was both our first times and we both had a blast, I had to let my inner child inside myself out and it was a blast.
Before my daughter started kindergarten I had her involved in swim lessons, tumbling, teeball, soccer, preschool it seems like alot and was usually only one or two activites going on a time but that also helped especially with her socializing and keeping busy. We did most of this through our YMCA which was a lifesaver. When she got to kindergarten she had no seperation anxiety and did really good.
Just keep your little guys day on a schedule and make it interesting as you can with lots of different things to go see, or explore or do. A variety of activities helps alot. The hardest part for me was winter time being cooped up in the house. Summertime is a breeze she runs around with all the kids outside and I simply sit and watch.
Good luck I promise it gets easier with age.