OP, I'm not going to waste my breath (figuratively speaking) telling you what everyone else has told you, because in your heart and brain you already know all of this. What I am much more worried about for you (and many others on this thread have touched on this too), is why are you still with this man? You have previoisly told us that he cheats on you - are you sure about that OP, he sounds screwed up enough to think that you thinking all these other woman find him attractive and interesting enough to sleep with him, is a positive for him, and you haven't left him, so did that work for you? I do not mean that as an insult to you OP, because I don't think you are stupid, (far from it, you come across as being an intelligent humam being), but I do think that you must have very low self-esteem, and also that you believe that you could not function without a man in your life, and that no other man could possibly find you attractive (I really hope that I am not just projecting here, as I spent many of my younger years feeling just like that, but sadly I didn't acknowledge that to myself at the time). Does that hit any slight chords with you OP? If so, I truly believe that you would benefit from the right sort of counselling, so please start off with your GP if you like and trust her/him, because you deserve so much more than this manchild.
I cannot believe that you can be excited about the idea of living with this man until the day one of you dies. It would almost certainly mean you moving into his Mum's house, and you having no autonomy of your own. You would be forbidden to make your own decisions, you would never feel like it is your home, and that you could come and go as you pleased, or have any input to meal choices, decorating the house, buying furniture, or even being allowed to choose pictutres for the walls, or ornaments that you liked. I very much fear that you would increasingly - if not straight away - be expected to do all the cooking, cleaning, looking after your mother-in-law's personal/intimate care, and when she dies, you would still be expected to carry out all of the other chores, and eventually be your partners personal nurse if he ever needs one. I doubt that the house would ever have your name added to the deeds.
Even if your partner looks like a young Omar Sharif (showing my age and tastes here!), and has the sexual stamina of a raging bull, I would find it difficult to believe that your partner is a caring, considerate lover, who nearly always trys to make sure that you are both happy and satisfied with your joint lovemaking. However, if he is, maybe there could be a slight hope for a future with him, IF he agreed to intense and longterm therapy, because he realises that at the moment he is an inconsiderate, manipulative, controlling bully in every other aspect of his life.
Please don't waste your lifetime OP, this could well be the only one we get. Even if you don't at the moment believe that you deserve any better, or that you could attract anyone else, or that you could live the rest of your life without a partner, you Do deserve an awful lot better, you CAN absolutely attract other people, and if you CHOOSE, you could live the rest of your life without a partner, and be extremely happy/content. Once you have some counselling, so that you recognise your true worth, and throw yourself into developing any interests that you have, you will look back on your life now with probably some sadness at your own lack of self worth, but also with the contentment of knowing that you pulled yourself out of this miserable time, with a bit of help from professionals, and hopefully some friends and family, but you will be the one who did it, for yourself, without you, it could not have happened. If I am entirely wrong about you and your partner then you have my abject apologies, but you probably stopped reading this ages ago anyway! But if any of it does ring true, then please do help yourself by asking for help from others, and learning to believe in yourself x