How to discuss possible red flags with little sis?

Question

Ok, so I'm just looking for some help with how to talk to my sister. I don't want to be indelicate or insensitive as she can take things hard sometimes. She has been dating a guy for about a year now- she is 21 and he is 23. They have been mostly long-distance as she lives in Utah and he lives in Idaho and they are both in college so they kinda have to be where they are. They travel back and forth a bit over weekends to visit each other since they are close enough to do that. They actually met when they were both living out in Maryland for a while. He was adopted from China by a single mom, hasn't really had any "father-son" type relationships. (This is all just background so you can understand some of who he is). 
Anyway, they have been talking about marriage, logistics with him graduating, where they would live, etc... He is a great guy from what I have seen. Seems to adore my sister which I appreciate. He's a genuine guy who really seems to want to just do his best. The red flag for me is what appears to be a jealousy and possessiveness issue. Several months ago my sister was talking to him on the phone and mentioned that she had talked to a guy she knew, just a friend, over FB messenger. Her boyfriend asked her why she didn't tell the guy she had a boyfriend and was so mad that he hung up on her. My sister had just said that it never came up and it would probably seem presumptuous to her friend for her to say she has a boyfriend when the guy didn't seem like he was trying to ask her out or anything like that... She told how his hanging up hurt her and he made a gesture of surprising her with a visit and he had roses for her as an apology.
Then tonight at our family dinner my brother and sister in law were saying they had heard from my other brother who the boyfriend knows from their time in Maryland and is relatively close to,  that the boyfriend was telling my sister that he doesn't want her going to the gym, wearing makeup, stuff like that. Like he doesn't want other guys thinking she is pretty and giving her attention. That was concerning for me. Again, it's just what I heard and could be a misunderstanding, but I want to bring up this possible issue with my sister. I'm 11 years older than her and so I have always been protective of her and when I heard about these things that side of me came out. Sounds controlling and potentially abusive, and if it's true, I don't want her to get stuck in a marriage like that. 
If you made it through my novel, congratulations! 
What would you say, and how would you bring it up? TIA

Answer

Just gotta be straight up with her. She may not like what you have go say, but at least you did say something. It's gonna be awkward, but just say "hey, we gotta have a conversation about some concerning things I've heard from your bf. It's none of my business, but I thought I'd bring attention to it and check up on you because I don't want to see you in a harmful situation". Trust me, she'll understand sooner or later. If worse comes to worse, at least you know that you said something.

Answer

Show her. Plenty of materials online…. Pinterest google

Answer

I would just jump into it and say it as it is.
You've noticed some things that makes you worry. And it's not that you don't approve of the relationship, but you just want to be sure everything is good.
You can't do much else than present her with your concerns and then let her figure out the rest on her own 🤷🏻‍♀️
As hard as it is.

Answer

If you don’t want to pin-point towards her boyfriend specifically, I suggest an idea: 
Have a girls night, have wine or whatever y’all wanna drink/eat, and have all kinds of conversations, maybe even about boys etc. Then you can bring up the topic of red flags, green flags. And hopefully that can maybe help you realize that she’s experiencing some of those red flags in her relationship. 
This probably isn’t the best approach? I don’t know tbh. But it is an idea. 
That or you can just be upfront with her, not directly about him. But could sit her down and talk about what an unhealthy, toxic, abusive relationship is. And encourage her to open up to you, if she has any questions or concerns. 
I guess the best solution is to just have her knowledgeable of these types of red flags.

Answer

The first incident, I honestly can see his point. If my husband was chatting with a girl, just friends, but didnt nentioned hes married(or rewind, didnt mention me as his girlfriend....and you can easily do that casually by saying oh how was your weekend? Mine was good, my girlfriend and I did xyz) I would be pretty upset and suspicious as well. Opposite sex friends need to be well aware of your relationship status to make it clear theres a boundary there, even if theres been nothing between you at the moment....omitting your relationship status when youre in a serious relationship feels iffy to me.
Controlling where she goes and how she dresses etc is a different story. It's even more delicate because you heard it from a 3rd party. If she knows yall are discussing her relationship behind her back, even if it's for a good reason eg legitimate concern, she will likely get very defensive. If he is controlling, he can also use that as leverage to isolate her from you if she gets upset and tells him everyone is talking about us. If you have a good relationship with her, it is better to try to get her to confide in you and address it vs "people are talking about you and worried and so am I"

How to discuss possible red flags with little sis?

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