I want to compliment you on your ability to communicate what is going on with you. It seems like you are really clear about what the issues are and that's the major first step.
For me, your approach to relationships is probably more realistic and his approach may be a bit forced. It seems to me that it's virtually impossible to know whether or not a relationship is going to be compatible for the long term unless you just get into the relationship and see. The trust, respect, honesty and love develops over time.....or not. But it takes time to find that out and if a relationship doesn't work, you move on. Anyway, I guess it's frustrating and it must seem like he is just sabotaging every potential relationship......for some reason. I guess that would be a good thing to try to discover.....is there an actual unconcious reason why he is acting this way?? Has he changed his mind about a poly lifestyle? Is it a lifestyle he thinks he wants, but is finding (on some level) that he can't really live it, so he's finding all sorts of various reasons..... why this one isn't good enough, or your approach to this one isn't right etc. etc.
I just want to encourage you to continue to post because there are a lot of experienced people here and I'm sure you will get some good feedback.