Hey Rayek, please don't give up on this board because of one comment. We all have differing opinions here, and different needs for certain things to happen to feel comfortable and deal with jealousy.
However, I do get Mary's feeling you are Beth's "doting father." Sometimes when I am helping my gf get ready for a date, I feel less like a lover, and more maternal.
It's too bad M is so afraid to meet though, since it's important to you. Maybe she'll come around. You can't change her or force her though. All you can do is deal with your own issues.
You could have stayed at the bar. Maybe meeting her in your group of friends might've been a good neutral way to meet. Maybe not, but now you don't know.
BTW, M is B's secondary. A tertiary would be M's 3rd lover, if she were to have one. M is your metamour, and if B had a 3rd partner, s/he would also be your metamour.
I realize this is all new to you, and I wish you the best of luck as you proceed! It's a rollercoaster. Take care of yourself. Be kind and patient with all concerned.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags (poly, F, 61) loving miss pixi (poly, F, 39) since January 2009, living together since 2013
"Master," (mono, 36), miss pixi's Dom for 3 years