According to JW cult rules, they need to have 2 witnesses to a wrongdoing before they can take action.
They do have 2 witnesses: anonymous tattletale and your mom.
Result: a judicial committee will be started. You will be invited.
If you don't attend, most likely you'll be DF'ed in absentia, given that they have two witnesses to your breaking of cult rules.
If you do attend, you will be DF'ed as well unless you repent, which includes kicking you boyfriend out, visiting all meetings, and sharing all juicy sex details with the old men in the judicial committee.
I take it you don't want to kick your boyfriend out over cult rules? In fact, I hope you don't, because they have zero authority over your life.
In that case, don't attend the judicial committee as it is of no use.
Note that talking with the elders about this or attending the judicial committee is considered a sign that you still consider yourself subject to JW authority and rules, and thus increases your chance of being DFed.
If you do write a letter that states the elders, the congregation and the judicial committee have zero authority over you, and your personal life is none of their bussiness (without saying you're not a JW anymore), they might consider you faded, make a confidential record, and not DF you.
And do refer to some lawyer stuff as others mentioned: you have no authority over me, if you continue this harrrassment my lawyer will kick your ass. Or something like that.
Good luck. Hope it works out for you.
Dog I hate this cult :-(