I'm going to take an educated guess on what's transpired.
1. Someone overheard you saying "I'm going to text, or so and so texted me." At some point this person didn't get their way or got in trouble. Instead of owning up to whatever they used your relationship as a diversion. "So and so gets away with the same thing because they are friends with X." It's called deflecting. Instead of taking responsibility for a problem they shifted the blame.
2. Someone is jealous of you because they don't have a similar relationship and want one. They more than likely didn't plan on getting your boss in trouble. You were probably the target.
Unfortunately it's the superiors fault for ever allowing the relationship to happen.
3. They've watched the video cameras and noticed you guys spend a significant time talking to each other. If I was running a store I would watch the cameras every now and then. Not to monitor you, but to analyze certain things.
If I noticed a superior was spending a large chunk of time in personal conversations with someone I would look into it. I've noticed one of my team leads has been talking to me less lately too. I figure they had a similar talk. It was very off putting.
I was like what have I done to be treated like this? I think having a good relationship with all of your employees is a good thing regardless of status. Especially for longevity. People stay where they are happy. People stay where they feel safe and valued.
I've stayed at horrible jobs just because I liked a superior. Your boss could be worried about their job. They might not know how to fix the situation. If they think they are being watched I'm not surprised if the bluntness isn't over the top.
4. Your highest up boss is jealous of you. They see the relationship as potentially harmful to them. If he/she is a control freak they might want to break all bonds. This gives he/she all of the power.
It's much easier to manage individual people than groups of people. This is why most places don't hire family members. This is also why many places don't promote from within.
I really like Target, but relationship forming is bad there. It's frankly disturbing how little I know my managers. I see these people everyday, but I know nothing about them.
It makes it difficult to formulate a baseline. Baselines are important for communication. Unless you know someone's baseline you can't grasp if they are being mean, serious, funny, kidding, etc.... It's very difficult to form trust.
Because of this people might jump to conclusions or take things the wrong way. Conclusions like this are rarely positive. You might also grow to fear this person. We fear what we don't know. This works under certain management styles, but it never creates respect. It can create resentment and chaos within a team. It creates an eye for an eye situation. It's difficult to respect a person if you don't know them. If this person doesn't know me how can they respect me either?
I've been with Target for a similar amount of time as you. I find it strange my store doesn't have regular get together's. Does yours? Maybe I'm not getting the invites, but I have a feeling these outings just aren't happening. I agree friendships can blind judgement based on favoritism, but they can also help you see truth. If I really know a person then I know what they are capable of. Guests and team members make up stories all of the time hoping to score discounts or promotions. If you don't know someone you might rush judgments. We are more likely to believe a negative about someone if we don't know the person.
The other side of the coin is this. If no personal relationships exist within management the environment is very cut and dry. Everything is based on what is considered facts and metrics.
I don't agree with this personally because I find retail data/feedback unreliable. Some do.... It's like sports teams who sign players based on potential chemistry or sign players based on stats alone.
Both can win championships, but I think chemistry beats out stats any day. The best teams are teams that work together. Then again the Lakers won championships and Kobe and Shaq hated each others guts.
My guess is if you give this time things will get better. It's just at this time this person values keeping their job or getting promoted more than continuing the relationship. I might do the same thing. Especially if I felt like I couldn't control the situation. I hope things get better.