Co-workers

So my husband is the deputy manager in his job, however there's this girl who has recently slept with two other members of the management team multiple times AND my brother in law (who lives with us) on a few occasions my husband has let her stay over in the brother in laws bed while I've been unaware of this as I work until 11:30pm. Husband simply texts saying "hey B.I.N asked if .... Can say over, I said yes. See you when you get home" 
My problem is brother in law knows she is sleeping with multiple other men, and still goes there. But now she seams to be getting closer with my husband, they're always taking and texting and snapchatting. He won't let me near his phone, when I've told him how I feel he keeps telling me I'm acting crazy. 
We've also been TTC for 2 years and I misscarried last month during which time she had told me "I hope you loose the baby" once this my husband sruggs me off when I try to do the deed with him and he barely tells me what going on with his job etc. Anymore. He still talks to this girl dispite what she's said also! 
Am I being paranoid here? What should I do?