One name for you: Sheryl Paul. Please do check out her blog: http://conscious-transitions.com/blog/ and her work on transitions and anxiety and the various forms they can take. In particular, check out these articles that she has written that address your situation specifically:
http://conscious-transitions.com/engagement-anxiety-and-the-ex/
http://conscious-transitions.com/am-i-meant-to-be-with-my-ex/
http://www.huffingtonpost.in/entry/marriage-fear-engagement-afraid-tying-the-knot_b_2258114
She’s a voice of sanity and a god-send, and her work has benefitted me hugely. Go dive in to her wisdom, let it spark your own inner knowing, and be off on your adventure of evolution.
Though I run this site, it is not mine. It's ours. It's not about me. It's about us. Your stories and your wisdom are just as meaningful as mine. 