I know exactly how you feel. My wife and I have transitioned to a poly relationship a couple of years ago. It wasn't my idea, but I don' think I'd go back to the way things were even if I could. I've had similar problems finding women who understand where I'm coming from and what I'm looking for in a relationship. I'm not just looking for casual sex or a FWB relationship either, I'm looking for connection and a relationship. I'm not saying I would turn down a sexual relationship, but that certainly isn't my first choice. I wouldn't rule out single mothers, they aren't all looking for fathers for their children, and more often they have had lots of life experience and are more likely to be able to deal with the fact that any relationship you may have with them will be different. I'm frustrated too. I've recently met a great woman whom I really like, and she's totally confused about how to proceed with the situation and it's killing me. It's frustrating, so I feel where you're coming from. Only advice I have is don't give up on finding that woman who does understand what you are looking for and understands that love doesn't have to be exclusive and it can be inclusive.
-All you need is love