From your update OP, he does indeed want you to suck it up.
He knows well she's a bitch and a bully.
She's going to a lot of effort to be unkind to you.
As a much older woman, I would tell you to think very hard about going down the long road of having your feelings dismissed, being told you are sensitive...when you clearly are not, and committing your life to a man that is weak and scared of his big sister.
Having children and being tied to your partners family is a very long term commitment and MN is full of women who would tell you to run rather than get attached to a weak man and his nasty family......
You do know this now, it has been clearly conveyed to you, so your choices will be what you live with.
So many women on here did not have the benefit of this and have regrets.
There is a particular type of loneliness of being in a relationship with someone who dismisses your feelings.....a real palpable loneliness that makes you feel so invisible and unimportant in your own life.
Personally, there isn't a man alive worth walking open eyed in to a future like that.
He is showing you EXACTLY how important you are in the scheme of things.
Focus on your self esteem and where it's at, if you are inclined to ignore all of the above.
Either way, I wish you well