Should I Be Ashamed?

I am a divorced mother with an 18-year-old son living with me. He is good looking but shy. He has had dates but he says he is a virgin and I believe all he has done is probably kiss a girl. We have always been pretty open with each other, and while we both maintain our privacy there have been plenty of times he has walked in on me as I was getting out of the shower, or I've walked in his room to ask him something and he has been getting dressed. We've seen each other naked but we don't flaunt it. We just say "excuse me, sorry" and leave the room. Ever since he was about thirteen I had been meaning to have one of those "birds and bees" conversations with him as most fathers have with their sons. I guess I always dreaded it and always put it off. About a year ago I decided I had to tell him something! We sat in the living room and I asked him if he understood sex. He said "of course I do!" I apologized for putting this conversation off but I felt there were things he probably didn't understand and I wanted him to be sure he did, especially since he was starting to date girls. I could tell he was uncomfortable with his mother talking to him like this. He told me I needn't say anymore, he already knew. After that we talked about protection. Of course, he blew that line of conversation off too. I then asked him if he understood the female body, meaning what was where and what did what? At this question he paused and said he "thought he did." I asked him if he knew what a clitoris was and where it was located. He just said it was "down there somewhere." Now from here on, I don't know if what I did was really wrong...or OK or not. I told my son that he had seen me naked plenty of times and I was not all that shy about it. I told him I was going to show him what was what so he had some understanding of the female body. I stood and quickly got out of my summer clothes and sat beside him on the couch. His eyes popped wide open! I turned to face him and told him to look at my breasts. I explained the parts of the nipple and I asked him to feel my breasts and nipples. He tentatively reached over and felt my breasts and nipples. He asked me what girls really enjoyed concerning their breasts and I showed him how to gently feel them, and twirl the nipples, and I told him I couldn't speak for all women but most women liked to have their nipples licked and sucked too. I didn't ask him to do that though! Moving on, I leaned back against the armrest and spread my legs. I have hair on my vagina but I keep it pretty well trimmed, so he had a clear view of my vagina. He just sat there staring at it. I pointed out all the parts of my vagina to him. When I was explaining my clit, I told him this was a very erogenous place and women are pleasured by manipulation of the clitoris. He asked how, and I showed him and explained by rubbing my clitoris. I told him technically, I was masturbating by doing that. By the way, I could see a really nice sized erection in his pants by this point in time. He asked me if I ever masturbated and I told him I did, and not only that, many women masturbate just as men do. I was allowing myself to enjoy this a bit too much. It had been years since I had been with a man, yet this was my son and my mind was pulling me in two different directions. While he was exploring my vagina I asked him if he knew all the formal names of the parts of the penis. He said he thought he did. I asked him if he knew where the glans were and he said, no, not really. I asked him to remove his shorts and I would educate him on his own body. He sheepishly said, "I can't right now." I knew the problem. He was shy and didn't want his mom to know he was hard. I said "you have an erection, don't you?" He bashfully said he did. I said, that's OK, all the better. I told him to take his pants off. He stood and slipped his shorts and underwear off and he had a very nice full blown erection. I could tell he was really embarrassed. I told him it was perfectly normal for a man to become aroused looking at and feeling a woman's private parts as he had been doing. I reached over and took his very erect penis in my hand and explained all the parts and official names, and cupped his testicles and explained in full their function. I was still having those inner mental tugs of war, knowing this might be wrong, but also enjoying it. I allowed my hand to slip back up his hard shaft and gently stroked it. I asked him how often he masturbated and he told me all the time! I told him there was nothing wrong with that. I removed my hand finally and he simply replaced mine with his. I asked him if he felt like masturbating right then and there and he just nodded yes. I told him to go ahead and do it. I laid back down and began rubbing my clitoris and I watched him start jacking himself as he looked at my vagina. I couldn't believe I was masturbating with my own son! I watched him jack himself until he spurted his sperm, and I found some secret enjoyment in watching his facial expressions, and I was amazed at the amount of semen he spurted. It also excited me I'm ashamed to admit. I concentrated and gave myself an orgasm in a few minutes after that. We cleaned up and I told him most people would find what we did wrong, and especially me giving him a thorough tour of my body. He told me not to worry, he'd never tell anybody about that! It was as soon as the next day he was sitting on the couch and we were talking. I could see a nervousness in his face, and in almost a quivering voice, he said, " Mom, would you masturbate with me again?" I then saw him grasp his hard erection through his pants. I thought for a moment and all those positive and negative thoughts raced through my mind. "Sure, honey," I said. I stripped naked in front of him and he pulled his pants off, we took our positions and we again masturbated to full orgasm. We have progressed to me jacking him off and he fingering me and rubbing my clit to orgasm. He really loves me to lie beside him on the bed, up on one elbow, as I slowly jack him off with my free hand. He relaxes and closes his eyes until he spurts. He loves it. The thing I hate to admit is I like it too. I feel terrible on one hand, yet on the other hand I feel OK about it. Am I all wrong? Mixed up Mom here!