HELP...I am the non-ADD spouse and our marriage is on the rocks

A lot of the issues we have revolve around his ADD - Ritalin isn't working but right now it's the only thing we can afford, even with insurance the other meds are SO expensive!  Anyway, it has driven a huge wedge between us - I'm sure this issue isn't new to this forum.  I've not made the best decisions as a result of the frustration and stress from not knowing how to deal with his ADD.  I've even considered leaving but dammit, I love this man.  We separated a while back and I met someone else so that's been an issue too.  I don't want my marriage to end but I don't know how much more I can deal with and I don't want to be alone.  So, I've maintained contact with this guy...yes I know this doesn't help matters any...I know this.  I've promised not to but it seems that the more the ADD gets worse, the more contact with this guy increases.  I've deleted all ways of contact with him as of this morning and I am really going to try my hardest to figure out how to make my marriage work.  Working with kids who have AD/HD (ADD) is much easier than dealing with my husband.  I hate admitting any of this but I believe in being upfront if I want help or advice.  So, judge me if you want, but if you are living with an ADD spouse then maybe you can understand why things are as they are.  I'd much rather have my marriage in tact and the ADD in my husband controlled (it tends to raise his frustration level which leads to anger - at least he's not at the level he was when we separated) so we can be happy again.  I know he loves me, at least he says he does.  But because of my relationship issue, he doesn't feel that I am capable of changing either.  Sigh.  So...this is where I am this morning as I sit here typing this out and having my first cup of coffee.  I don't want to have an affair...I really want my marriage back.  But I am lonesome, frustrated, angry, and feeling lost right now.