Your poor heart has been broken. I am very sorry that you became involved with someone who wasn't available. Engagements are broken every day and if this man truly believes that you are a better partner for him, then one would expect him to bite the bullet and break off the engagement.
Here's where the real problem lies: This man isn't able to stand up to his parents. He obeys their wishes even at his own expense. In this respect, he hasn't grown up and emotionally separated from his parents, so, in actuality, he isn't even mature enough to marry anyone.
If you are still speaking to him, then tell him that we've identified his problem and ask him if he's willing to be a good son at his own expense. Ask him to talk to a therapist about the problem I've uncovered. This is all you can do.
If he seems to respond to what I said and takes action to work on his issue, then you can feel encouraged. If he hems and haws and doesn't take the ball and run with it, then you will need to grieve and let him go.
You can't keep on the way you've been living. Your caught in limbo, yearning for a man who is himself stuck. If he doesn't begin to work on himself, you will be left with no choice but to move on and create new friends and new attachments.
In the future, please make sure to use my online consultations in order to protect yourself from becoming involved with someone who isn't emotionally ready for a relationship. One of my consults is called'Why is My Relationship with Him/Her on the Rocks.' This consult assesses whether the person you are interested in is actually ready for relationship.
You want to find this out before you give your heart away. Your heart is too sensitive and beautiful to be subjected to emotional experiments. Let me know what happens to you.