<human>: Hello! Hope you're all having a good morning! 

I'm 21 f, been set on being child free since I was a preteen and my mind hasn't changed at all since then. My brother is 25 M and his wife is 24 f, has one daughter who is 5 months old(result of fling she had when they were on a break but he forgave her, it's water under the bridge now. My brother adopted her.).

Now to the story and my pent up feelings, My brother just told me his wife is pregnant. My first reaction was "oh... how do you know it's yours?"

He grew uncomfortable but told me the timeline aligned with him being home and her old birth control expiring. They grew lazy in using protection and didn't mind getting pregnant. The reason why I had blurted out the rude question was because when his wife had their first child, he was devastated when he found out the baby wasn't his. It wasn't cheating since they were separated and on non speaking terms at the time of the fling but they had started talking immediately after the fling had ended and had had sex. 
So emotions be damned, he accepted the pregnancy and adopted the girl, my niece.

I have been skeptical of my sister in law since day one. She cheated on my brother since they dated in high school, and like a masochist, he kept taking her back. When they graduated, she kept up the cheating and lo and behold, my brother took her back. They got married and when she slept with a mutual friend and he finally left her. But after a few months, he said he needed her and took her back.

I know this new pregnancy is my brothers since the times align perfectly and his wife hasn't even gone out with friends or family since the first baby was born. But, a part of me feels doom and gloom for my brother. A part of me is happy he'll finally get his own child but I feel like once this baby is born he'll be stuck forever.

Can anyone relate??

Give me a shortened version of the text
<bot>: sister in law is pregnant again. I reacted skeptically due to sister in laws shady past. Brother thinks I'm a bitch now. How do I show support despite my skepticism?