I agree with your T, it would have been healthier to go away.
As it is, you're trying to "catch him" disobeying or being disloyal, and you're watching them like a hawk. I can feel the tension in the house through my monitor!
This is not healthy, this vigilant spying and obsessing, it really isn't, Lupe. You are not achieving anything but more instability and more damage to the relationship. It is damaging for one adult to treat another like a bad child.
It's true that it takes a long time to find out if someone is trustworthy.
Unfortunately, it may take even longer to find out if you can experience trust.
The thing is, even if you can set up a thousand "tests" or "traps" or "proofs" -- ultimately, your inability to be at peace alone, or happy with your own self, leaks into whatever relationship you're in. They're really all the same, at heart. The previous bf and his dancing with other woman, your son's gf's family/mother, your coworkers at the previous job and now this job...
It's all the same theme. It's about YOU not trusting that you can create happiness and meaning without a whole lot of reinforcement from outside sources. And because of your mother, outside sources feel so profoundly unreliable and unsafe to you, that you go into hyper-controlling, hyper-supervising mode...
Which snuffs out the possibility of building a healthy intimacy. Not just an intimacy that exists when it's the two of you alone under the moon, or one-on-one with anyone...but a healthy ebb-and-flow closeness and feeling of belonging that you carry all the time, especially while alone. So when you are interacting with other people--family, bfs, coworkers, public--you don't have to be afraid...and the natural triangular interactions that are part of being in the human community don't all feel to you like a competition.
You will know that there are good human beings all around, a few who aren't, but there are many who are good and nondestructive, so the world of connecting is a place of delight, not terror. And that if one connection doesn't have a feeling of ease and oxygen, you can release it without so much anguish and blame, and move forward in the world knowing that there is PLENTY of love, no shortage of it, ever, and soon the universe will offer you a new opportunity to share it. Maybe in the ways you fantasize about or pre-define, or maybe in situations you've never encountered before.
I have finally recognized that there was a whole lot of wisdom in the old-fashioned "stages of courtship" and taking a VERY long time to get to know someone, particularly before becoming sexual (which often bonds you whether you are ready for that bond or not...thank the hormones).
I think I'd find it unsettling to have a bf who's still enmeshed with his ex. I don't think it's strange to be troubled by it.
But I do think the tests and proofs and invisible Lupita-cams (mental ones) are not the solution.
You're torturing yourself. You could be walking by the beach, enjoying a museum, or at the movies.
Matter of fact, I'm going off to a movie by myself this afternoon, and can't wait...
Love to you, Lup, hope some of this helps a little.
xo
Hops