I have a bipolar DD and was married to a probably bipolar individual for 8 years. You will NOT change him, you will NOT alter his behavior, you will NOT fix him, you will NOT save him. Sorry, nope, no amount of giving, loving, cajoling, coddling, forgiving on your part will do any of those things. The meds MAY help, but only if he is fully compliant and only if they are the right meds and only if they are in the right dosages.
Sex addiction is a tough one to crack and sex addiction while bipolar is REALLY tough to crack. Online, offline, phone, back seats of cars, whatever it's all a part of sex addiction and YOU will not make it go away. In my situation, it started out with Playboy, progressed to hardcore, on to strip clubs, then a hooker with a disease (which he then gave to ME, 2 actually, one of which may kill me with cervical cancer someday), and finally child molestation of my (and his) oldest DD. I'm not saying that everyone follows that progression, but it is NOT uncommon (according to all the counselors/psychologists/psychiatrists I've dealt with) and it is a reality that many have to live with.
Lying becomes a high in and of itself. Even when they are "caught" in the lies, they frequentely don't acknowledge it, b/c they live in a different reality from the rest of us. Sadly, women like you (and like I used to be) live on the edge of that reality, too, and it is VERY difficult to listen to what other people are telling you. It's also very difficult to make that jump when you are dependent on someone for your finances. It's not going to get any better, so you need to cut your losses (of time, emotions, finances) and get on with your life. eBay, find some freelance work, tutor, sell Avon, whatever, but get yourself out and get some fresh air and wake up out of the situation he has you in. When you can support yourself and take pride in yourself and realize that YOU ARE WORTH IT, then the right man will come along and make you his princess. I agree, it's hard enough to have a good relationship with a good man. Also, you are marrying his WHOLE family and his family history and possibly condemning your own children to being bipolar (or just having to live with one).