OP
I've read through your post - please listen to what people are telling you.
Leave this man now. THIS MINUTE!
If you marry him you will be stepping into a life of abuse of all kinds - physical, mental, emotional and financial, and he will cut you off from family and friends so that you have no-one to turn to for help and support when the day comes when you try to get out of the marriage - possibly with a couple of babies in your arms!
It doesn't matter what he tells people, or how much he blackens your name or your sister's - none of that is worth your first black eye or broken jaw; none of it is worth being raped within your marriage; none of it is worth being isolated from the people who REALLY love you.
You aren't a bad person - you are just very naive and I think you don't realise that he is, at present on his good behaviour. Think of that. When you are married and you are committed to him, he will stop being "nice" and will really start to behave badly.
Can you imagine what he is going to be like, if this is how he treats you now? Your life, and your children's lives will be HELL. There is no other word for it. You will have no life of your own at all - you will be his slave and his punch-bag.
He is an awful, horrible person. Please listen, pack your things and go home to your family. If you lose face - so what?! At least you keep it in one piece.
He goaded your sister into responding to him, and he did it in the most horrible way imaginable. He wants a reason to stop you seeing your family. He wants you isolated and alone. He wants to control everything you do.
Please leave. Don't tell him you're leaving, just wait until he's out, pack your stuff and go. And thank your sister from the bottom of your heart because she's obviously seen through him, and has now helped you to see him as he is.
I know it isn't easy - I appreciate you may be frightened of him - but please, please - don't end up as a statistic on the battered women list.