S.G.
is it in the decree that no over night visits are allowed with someone of the opposite gender, if so, there is nothing they can do. a lot of decree's are having that listed these days. I'd make bf move out before you take him to court, my husband was holding that against his ex wife and she lost a lot of her case (that is still going) because of that reason....the court systems frown on that about as bad as not paying child support BIG TIME.
over night visits at that age are not bad. i left my exhusband when our daughter was only 3 months old, and well, judge saw no harm in it mainly because i was no longer breast feeding.
i'd surely call an attorney and talk about your rights but with joint custody, he has just as much say so as you do, that's what i have with my ex husband...what they enforce is up to them.
MAKE A JOURNAL of what's going on so when court date arrives you can tell exactly when what happened. and let him keep making the "wrong moves" holding her hostage or what not, it'll make him look worse and worse. i had to go through all that with my ex and he's now set himself up that i now qualify to take him for child support and possibly custody too (took 8 years but it worked itself out)