This is typical behaviour. Someone repeats a rumour to an elder and then they go asking questions of others to try and verify the rumour. By JWs own interpretation of the bible it's not scriptural.
The scriptural (if you really want to call it that) process is that the person who first comes up with the information should approach the person and only go to the elders if the person does not listen to them.
The elders should then approach the person and find out the facts.
In cases like this the original person who comes up with the info either does not exist or the elders know it's all just a rumour. Instead of telling the person to go and approach the one supposedly doing wrong, they try and find out more using sneaky techniques or by pressing others (e.g. your mum).
Your mum could just have easily said it's not of her business and the elders should approach you directly. She could have asked them why they are only interested in you now, she's not heard them asking after you or trying to go and encourage you as lost sheep for the past months. She could have accused them of listening to baseless gossip and not following scriptural processes.
Instead she did what most sheeples do in this circumstance and fessed up, thereby making the job of the elders a doddle.
So now they have you where they want you. If you accept the JW process then you meet for a JC and unless you change things you will be disfellowshipped. If you don't bother then you will be disfellowshipped anyway.
I know some, but not all, have avoided the actual formality of disfellowshipping after threatening legal action but the result is very likely to be the same. Unless your lawyer is very, very good the elders will make it known what your situation is and people will shun you.
Rather than worrying about it I would try to be positive. By moving in with your boyfriend you must have considered what would happen when the elders found out so I would just lance the boil as quickly as possible. Do the legal thing if you really want to but either way get it over and done with quickly and move on.