After the end of my marriage. How do I trust enough to commit again?

My marriage fell apart after 10 happy years. After the birth of my second child my partner changed. Became disinterested in us, found something with my 'friend', treated me badly for 6 months before I funded her move out.

Nearly 2 years later I find myself dating an amazing, loving woman who wants to build a future with me. So why do I find myself stuck. Unable to make any long lasting decisions or commitments to her? I feel so inept, scared of what is to come.

Any advice, ideas, anything really. Much appreciated.