PLEASE help me put this into the proper perspective

Synopsis of situation: I am a widow of 7 years. Significant Other (SO) is a widower of 2.25 years with AD/HD which has never been dx'd or treated. (It slowly dawned on me that this was the case, and has become clearer over time and from discussions with the boys' teachers and caretakers, reading the boys' various medical, school, psychological records - his late wife was aware and it was apparently a much-discussed issue among them).

SO has twin autistic sons, 18 years of age, both of whom have AD/HD issues, and a daughter, now 21, who has AD/HD. We met in March of 2013 and became engaged in October of 2013. I moved in with him in February of 2014, but had been staying here much of the time after we became engaged.

SO does have a successful business. When his wife was alive, she took over all of the bookkeeping and bill-paying duties, enabling him to stay afloat and take care of the business. Since her death, things have deteriorated greatly in that arena. Bills don't get paid in a timely manner, his billing of customers doesn't get done, and the piles of papers are staggering. He spends a lot of time apologizing to his customers for being late, lying to creditors ("I never got the bill!"), etc. He did try hiring two people to help - his DD and a family friend - neither of whom have worked out.

Now, don't get me wrong - there ARE a lot of crisis situations around here surrounding the boys, who can be verbally and physically aggressive... so some of his inability to be on time, etc. is very justified. I've been punched, kicked, bitten, gone after with a knife a couple of times - but the boys had VERY little structure and consistency in their lives before I was here. They have greatly improved - and SO has gotten over a lot of his denial about their behaviors, finally agreed that one of them needs to be on some pretty potent medication, etc. They now have schedules, they are no longer allowed to watch violent/inappropriate media or play violent video games, their media time is now an earned privilege. They are doing MUCH better socially and behaviorally, and the home is much more peaceful.  SO was very resistant at first, saying he could not be as consistent as I was, even if he knew that it was the best thing for the boys - he came around eventually.

I've spent hundreds of hours filling out forms for them, taking them to appointments, meeting with people from the school, talking to their caretakers, therapists, doctors, etc., developing systems for them, taking care of them. I've gone to seminars, bought many books so I could learn more about autism and AD/HD and nonverbal learning disorders. I've paid to take classes.

Two weeks ago, SO dropped a bomb. We were planning to be married in September. He didn't want to marry me yet. His reasons were pretty vague - worries about finances, his life is just too chaotic and he has to find a group home for at least one of the boys, etc. Okay, so be it... but then he said I'd rushed him into this... at which point I took off the ring and gave it back.

A few days later, I'd been working on the boys' computer at SO's request, trying to figure out some Net Nanny issues. I discovered that he has been (at least since May) cruising a particular dating site. At first I thought it was one of the boys, or perhaps my son... but it took only one look at one of the profiles SO had been looking at to realize that it was him. I was FURIOUS. When I confronted him, he tried denying/lying, but finally admitted it. His crazy logic (?) was something about finances - but I think even he doesn't know why - I think it was an impulsive thing that turned into a compulsion.

Whatever. It got us in to see a therapist. She advised me/us not to make any rash decisions. I had been ready to just pretty much walk out, though I wanted very much to make sure SO was set up to get help and the boys would be prepared as well as I/we could get them prepared. That's the part that breaks my heart the most, I think - the boys.

The therapist fast-tracked SO into seeing an AD/HD therapist, whom he's made an appointment to see next week. He doesn't want me involved in the therapy.

I've been trying to UNDERSTAND all of this stuff he's saying. I've tried to ferret out his reasoning. He'll say something, I'll say, "So you're saying X", then he will say, "No, it's not like that" - again, maybe he doesn't even know why.

I've started writing things down that he says in these conversations - because I have some very serious decisions to make, a fixed income (sufficient to live on, certainly, but fixed)... and I do NOT like feeling like he has me over a barrel and I cannot leave.

Today he has said:

1. "It's too soon"

2. He doesn't want any more to "take care of"

3. Money worries; he wants to save for retirement

4. He "can't take more on"

5. "I need to have less responsibility in taking care of others"

6. "DD is launched, and the boys will be"

7. "I need to just take care of ME"

Last night, it was, "Who will take care of ME if something happens?"

To me, this all sounds like part midlife crisis, part AD/HD, part fears of the future.

I asked him, "If you were in my place, what would you think/do after hearing all of this?"

"Well, I'd have done some things differently. I'd offer to pay an electric bill. I'd buy a bag of groceries without being asked, so I didn't feel like a mooch."

I blew. I have offered REPEATEDLY to help with things and he has ALWAYS said no, he has no need of my money. I've done it anyway... bought a few groceries, bought him nice gifts, refused to let him help with paying for my gas as he offered, paid for entertainment and meals (nice places, expensive tickets etc.). He'd sometimes just transfer money into my checking account when I didn't even WANT him to.

He apologized but the damage is done. I think he really sees me as a "mooch" and I am NOT willing to stay here under those circumstances. Last week when he said he thinks I should pay for some of the expenses I immediately wrote him a check. I would never have had a problem doing so, but he refused to take anything - he'd say, "I have 30k in my checking account - I don't need your money!".

So "don't do anything rash" - well, I'm getting pretty worried that I am going to fall apart. I cannot stand the thought that he thinks I am taking advantage of him. I don't know it it is just stuff he's blurted out - I don't think so, because of all the other things he has been saying... I cannot STAND it. I was with my husband for 34 years and I was the major breadwinner. We had a good marriage, and were very much in love for the whole 34 years. We were still passionate and looking forward to retiring. It wasn't easy all of the time (he was bipolar) but I wouldn't trade a moment of it.

So yeah, I know what it's like to be a caretaker.

I can't figure out what SO is thinking or feeling exactly, because he will say something and then deny it, but to me it sounds like it's something that yeah, HE needs to get figured out ON HIS OWN - and until he does, he has no business being in a relationship.

HELP! Am I seeing this wrong?