OP. PLEASE do not get sucked into this. You are worth MORE than being second best. To anyone. And much less to someone who is meant to love you.
It took me 12 long fucking years to stand up for myself and put my foot down where my MIL was concerned. It was only then that I realised how much she had controlled my life.
Your husband is emotionally abusing you. You may not see it, but he is. The threats to leave if you go on this trip? Emotional abuse.
He is so sure you won't leave him that he feels he can treat you like a possession.
Please don't waste 13 years of your life on someone like this. You will NEVER come first. He isn't going to magically change himself.
When a man tells you who he really is - LISTEN.
Your DH is telling you that you will never come first to him, you are not important to him, and you will do as he says.
You deserve better than that. So did I. It just took me a bloody long time to realise that.
Listen to your DM too. SHE is worried about your relationship and how your DH and your inlaws are treating you.
No one (except your nasty inlaws, and who cares what they think) will think any less of you for standing up for yourself, even if that DOES make him leave, that is a reflection on HIS lack of character, not yours. It shows him to be the controlling twerp he really is.
And it shows you for being someone who knows their own worth, because no one deserves to be treated like a chattel, something to be dragged around to satisfy her husband's every whim, and that of his family.
His mother has you leaving YOUR OWN HOME when she comes to see 'her son'. Because she makes you feel so uncomfortable.
I put up with being ignored in my own home for 12 years until I finally snapped, and told the ex-MIL a few home truths about her rudeness. And told her to get out of my home until SHE could apologise to ME.
My ex had the tearful phone calls about how horrid I was, and how I needed to apologise to her etc - I told him that would be happening when Hell froze over, and she was no longer welcome in my home until she would treat me with respect, and apologise for her rudeness.
He told me that he would leave if I didn't apologise to her for upsetting her. I pointed to the door and said "Go on then, the door's there..."
It took 13 wasted years to get to that point. The only good thing to come from that relationship was my DC's and me finding my own sense of self-worth, and what I would and wouldn't put up with in a relationship.
My Ex-MIL, on finding out that I was pregnant with DC4, told my Ex (not realising I was sitting close enough to him to hear, as I knew he would be upset by whatever she said, and wanted to comfort him) to leave me. Whilst I was pregnant.
BITCH.