Normally we get alot of questions from women, in love with a man who is still with his wife/exwife with kids etc, and he won't leave due to a case of indecision,
Normally the best advise to give is "Keep the relationship open with him, but don't get your hopes up & look for someone else..."
This advise is relevant here but the situation doesn't seem so clear cut. This man seems very responsible, he obviously has some emotional investment in his ex, and obviously wants to take care of her so nothing bad happens to her, which is very admirable.
However this could take years or never happen... but don't think you have to rush your life, its not a game, you don't "complete it" and you don't need to.
Looking objectively at this, how happy are you? are you the happiest you have ever been? are you downright miserable?
Does he give you what you need? (notice I didn't say does he give you "everything you could possibly want"!).
After you answer these questions you'll know what to do.
Whether you should keep on as your going or "just hope" while looking for another... its your decision.
You'll feel weird looking for one, but it can't do any harm looking for another guy!
Hey why not start now and hope you feel silly in the future for doing such a silly uneeded thing... instead of waiting and in the end regretting what you didn't do?