Every long terms sexual relationship has a kick start, an increasing high momentum leading to a plateau phase and then it innevitably experiences a decline to a more stable or routine level. It is possible that you have overworked your expectations from such a relationship - for instance, should you be feeling secure or insecure, loved or unloved based on your sexual life? Don't listen to magazines and people, if a relationship is to survive it has to move from passionate (infatuation, constantly thinking of the other) to what social-psychologists call "compassionate" love (i.e. friendship, companionship). If you entered a sexual relationship instantly (i.e. on the same night you met him) it may be that you have woven your whole "love story" based on the physical aspect of it without having let the romance blossomed to maturity first; so while you may still be belating-mongering he may have already dropped down from plateau to compassionate level. The logic behind this is that given the fact that he does cooperate when you ask him to do things and does managed to soothe you by telling you "the right thing to calm you down" indicate that he does still have some kind of socio-psychic connection to you nonetheless.
Don't worry about him doesn't know where things are and stuffs like that; if you had had enough time to know him first you would have had the opportunity of recognising these flaws beforehand and it would probably not have changed a thing - tell most women the way their prospective fiancés live isn't conduisive to a healthy household and they still go ahead to embrace these men preferring to think: "he isn't like that!" For your part it is not an exaggeration to say that most men are like that. Again you wouldn't want him to be an obsessive perfectionist or "control freak" either you are making an attribution of his lack of such behaviours to his "lack of interests in you" as perceived by you, very much in the same way many women feel insecure when they feel their men aren't as jealous as they would wish them to be even though we men are socialised everyday to believe that a control freak is abusive and pathetic!
As for the sex, there may be a variety of explanations to explain it, some of which have already been hinted from above. But then again we cannot possibly solve such a complex issue here, especially since we don't even have his point of view - to be objective. How far would you be willing to go with this man now that you are about to marry and already have a baby with him? Would you mind masturbating as long as everything else is fine? Would you be willing to revise your kinky threshold levels? It is not so much the lack of sex that is bothering you most, but rather the quality of the sex itself it seems. Unfortunately we don't have his side of the story and this is quite complex. Could it be stress at his work? Could he be depressed? Is he taking any medication? Could it be a logistics issue - perhaps morning session would be better? Who can tell...?
Or is it deeper than a sex issue? Sometimes men are indecisive about commitment but somehow got dragged into one. Lead by their pennis' needs, a man would say anything a woman wants and needs to hear and suddenly he wakes up in a situation he doesn't even know how he got himself into. I wouldn't fear about a mistress if I were you. It takes a lot out of the other woman to uproot a man away from a loving wife no matter how old the wife is but especially if she's younger and beautiful.
I would suggest among other things that you two take some time off. Go on hollidays or something and make it about the two of you [leave the babies at grandmas']. Don't make it about sex - if it happens fine, if not fine. Make it about rediscovering yourself and him. Find and discover new things that you like and that he likes. Find things you would like doing together or visiting together other than sex.
I can only wish you good luck. Hope you find your way.
Finally, I am getting the sexual satisfaction that I deserve from real men!