I just wrote out a huge long reply then hit the back button and lost it. Sorry if I seem rushed, I'm frustrated with my computer

Ok. Here we go again.

I think individual counselling is a great start. Most times childhood issues don't go away on their own and will cause problems later on. That being said, I have a few ideas on lower cost counselling
1) I used to work for our local region, in the accounting department. The region covered $95 (usually) of the counselling fees, while I think the attendee covered the other $15 or so. Contact your region or city and see if they have any options similar. Ask about counselling and family services, they often have fees geared to your income
2) If you do attend AA (great idea) (also check out recoverynation.com) the hosts may be able to refer you to additional counselling options
3) If you have a local college/university, psychology grad students are required to do unpaid counselling work before getting licensed. They already have their masters and are working on a Phd so they are usually fairly qualified. Sometimes they have a supervisor working directly with them
4) If you are working, check to see if your employer has an EAP (employee assistance plan). They are separate from insurance coverage and very underused by employees. Essentially it's a phone number/website that you can access if you need someone to listen, referrals to counselling, basic advice, it depends on the company the EAP is with and how qualified their employees are.
5) Group counselling is always cheaper than individual counselling. While it may not get through all of your past issues, it can help with things like self-esteem, coping habits, boundaries etc

As for the sex life, it seems like there are a number of issues all colliding.
1) (I'm getting carried away with lists) Sexual abuse usually creates either (or both) hyper-sexualism (extremely frequent sex, or "deviant" sexuality -this could be one night stands, extramarital affairs, etc), or avoiding sex (low sex drive, fear of intimacy/loss of control). Have you talked to your husband about your past relationship and how it might affect you presently?
2) Yes, it could be a hormonal issue that is lowering your sex drive. Many medications (birth control, psychological meds, etc) can cause this, or just natural imbalances, which the doctor can help re-balance
3) Sexual needs are often under-communicated between men an women. Now this is a generalization and by no means am I saying this is always the case. But often times, men just need that testosterone to want sex; sex drive is physical. On the other hand, women frequently need emotional stimulation as well and the physical desire. So his "lack of romanticism could be an issue
4) Feeling pressured often decreases desire. If you feel like you are doing it because you are "supposed" to kind of takes away from it.
5) Yes, your having sexual acts outside of the marriage, may play of some of his sex drive as well. He could be trying to have more sex to "reclaim" you. I don't mean this in a controlling way, more as a way to get the picture of you with someone else out of his head by replacing it with a new one -which can take a looong time (based on personal experience) especially if you were doing these things with others and not him -it's just hard to comprehend.

I think once you are on your way to making yourself a healthier person (and by the way, I think you are doing a great job already) you'll be more comfortable setting personal boundaries. Like "I'm very truly sorry for what I've done in the past and the pain I've caused. I'm doing this and this to make myself a better person, wife and mother. But I also need for you to ____." From my marriage counsellor "when you ____, I feel ____, I need_____" is the key to stating boundaries.

Despite what you've done and the guilt you feel, you still have the option to make choices regarding the marriage. Choosing to go elsewhere while married was a bad choice, you know that. But you do have other choices, which can be to require marriage counselling. Explain to him what YOU think you could get out of the counselling. Don't make it all about his gaming, smoking, but include things like "I want to be able to find ways to communicate without it turning into a fight". If he's not willing to meet your needs, you also have the right to choose not to be married to him.

Sorry that got long, and I'm sorry for the situation you find yourself in. Keep doing what you need to to keep you and your kids safe and healthy