My 1989 ford bronco ii will moved forward when put in into reverse?

Also, my ex has sabotaged my auto for
awhile (in his attempts at getting the "needs
to be needed" feeling he so very much
needs...)... so I am assuming he did do
something to my bronco ii. I just bought it
and the reverse although it did slip one time
the day i got it. But in this circumstance, it
went forward a milisecond and then moved
forward. Now, howevr, it's stuck at the end
of my driveway and blocking people from
walking on the sidewalk and having a clear
path. How can I fix this and quickly ? I  am
desperate to do so now. Thank you. Kristina