OMG, I read this, and I just want to give you a shake.
You don't want to believe what some Posters are telling you, but you are young, and you need to remember that a lot of women on here have more life experience, and are only saying these things to help you.
So, as someone who is 20 years older than you, and who has been around the block, I'm going to give you my two pennies, and you can do what you will with it.
I don't think he fancies you. I don't think he fancies women at all, actually, because any man with half a sex drive, would eventually shag a woman he shared a bed with, regardless of how sexy he found her, because his natural urges would take over.
So, he's either asexual, gay or into something else entirely, and (much as I hate to say it), a horrible thought crossed my mind when you said that he worked with disabled children, for virtually no pay.
I think you were vulnerable when you met him (otherwise there's no way you would have moved him in, when you felt he didn't desire you), I think he picked up on that vulnerability, and saw you as an easy meal ticket.
He doesn't love you, or care for you. This is borne out by his actions : sponging off you financially, and not caring about your feelings, wants or desires. You are his meal ticket, and nothing more. He has to stay reasonably friendly with you, because you hold the purse strings.
You wouldn't allow a sibling or a female friend to move in to your home, and pay no rent. Why are you letting him do this? Some women overlook a man paying his way, because they love the man and get great sex. I couldn't stand for that personally, but in this scenario, you aren't even getting the sex, or even affection. As for saliva smelling, he sounds positively unhinged.
I don't believe this his mother having an affair caused his sex drive to disappear. Quite frankly that's a crock, but he's done such a number on you, that you are actually willing to believe this.
I also think that if you got sick, and lost your job, he would suddenly do a fantastic impression of the Road Runner.
Despite all of the above, the situation is untenable, unless you are prepared to become celibate at 30, and support this "man" for the rest of your life. Are you? Because if you're not, every day that you spend with him, you are not actively moving forward.
What would I do? I'd send him back to his mothers, and start dating again. Date solvent, nice normal men only, who aren't plagued by multiple issues.
You could have a normal life, with equal financial responsibility, dates out, holidays, mind blowing sex and maybe even another baby, if that's what you want. It's all there for the taking. But only once you get rid of this piss taker.