My son and i... [is it normal?]

I am a 30-something-year-old woman. I like to think I look good for my age, do my best to stay in shape. I divorced my husband of 11 years, two years ago. He was not particularly good to me, it started out sweet but quickly turned sour. He left me with two children, an older son who moved to be in NZ and a younger son, (17 now), who I won't name of course. Anyway, He lives with me currently, he hasn't got a girlfriend.
My son is kind and sweet and we maintained a good relationship (I'm quite shaken currently), I would say but I have been noticing his sexuality more and more these past two years, a little after his father left the household.

I have found my used panties in his room, sticky with his... well... cum, sperm, whatever you want to call it, in/on them.

I see him erect around me more often. (though I don't think I'm the cause; I raised my children well, they respect woman and I was quite liberal and comfortable being naked around them.)

He frequents porn sites (I know this because I hear it at night).

I have spoken to a lot of mothers and professionals about this behaviour and it's pretty common, if not normal, even if some would deny it. I haven't confronted him about is because I don't mind, maybe a just a little with the panties. I wonder if he smells them...
That's not good, I should probably talk to him?

Last week, my son and I were sitting on the couch after dinner (we cook together, he's quite good at it!) watching a movie (Interstellar), I'm a bit of a nerd, as is he; we play video games together often and watch at least one movie together in a day.
I work from home and he only has college 3 days a week, so we spend a lot of time together.
So anyway, the film is nearing its end and I'm leaning upon his shoulder. I assume he thought I'd fallen asleep and he kind of went for a grope of my chest. My breasts aren't particularly big, I'm quite a small woman (5'2) but he gave them a squeeze all the same.
I will admit it felt good, to be touched like that, I haven't since my husband and I split.

I sat upright after & gave a pretty stern look, I wasn't really angry. Just shocked.
This was his first advance on me but not his last.

I should also come clean about something I did. Highly inappropriate but I couldn't help myself. I once tasted his cum from my underwear. It was surprisingly sweet, cold, as it had been a while after he'd made his mess. I sort of regret it?

Anyway, his best friend just had his 18th birthday (This Monday) and they had all gone out for the day.

So my son rocks up to the door at about 2AM on Tuesday morning after. Clearly been drinking, which is fine by me. I won't let him smoke, but I've taught him how to drink safely. He gives me the biggest hug and tells me he loves me and comes inside.
He's not blind drunk, just a little woozy I'd say & I had a few glasses of wine that night while playing Hearthstone.

We sit on the couch, cuddle some. I'm not sure how, but his head ends up in my lap.
I'm only wearing shorts and a tee, at the time I didn't see a problem with his behaviour so I went back to my game while he seemingly took a nap. Nothing bad about that?

My issue, at least I think he was doing it, might just be my overactive imagination...
I think he was sniffing me, he wasn't face down in my lap, but he had turned his head in towards me more. I couldn't really tell if he was asleep or not, he could have been snoring lightly for all I know, so I never said anything about it. Should I have?

The bad part is that after he decided to move and go to bed (after about an hour of what may or may not have been him sniffing at my cunt) I was really, really wet...
Come morning he doesn't say anything but I feel myself getting red-faced around him over breakfast.

It's Sunday morning here as I write this, my son has been himself, with a little more frequency in masturbation. He also walked in on me using the bathroom on Thursday evening but I honestly think that was an accident. Right? He couldn't be that perverse as to get his rocks off from seeing me pee...

I haven't confronted him still, but this has been brewing over in my mind, so here I am confessing my sins.
I think about him at night, even touch myself...
He's my son and it's wrong, isn't it? I'm lonely and I think he might be using that...
But that doesn't make me want... or fantasise any less.
What should I do?

[I'll update if I can]