Re: your Houston ordeal ... I can sure relate. I'll never forget the time my wife and I went to the theater (which was unheard-of for us) to see "The Two Towers" when it came out, had this lovely time watching the movie, and then exited the theater to find the back window of our car smashed in, with the brick used to smash it sitting on the back seat.
That's really scary that they got your host's driver's license. Crikey, she should actually consider moving to a new domicile so as to get a new address! I sure hope they catch the burglar that did it.
Re: the Kensi files ... it's astonishing that Matt was willing to meet with her at all, and while relations remain strained, at least y'all established that she and he can (under the right circumstances) converse civilly without causing a scene. I'm glad that worked out.
It's cool that you are building a new friendship with her and getting some counseling to help. Sort of like getting closure on the situation.
Re: your best friend ... can you tell her that you're only turning down the offer for romance because you want to be monogamous with Matt? Perhaps that would help her feel better, like she wouldn't feel like it was something about her personally that you were rejecting.
I seem to recall that Matt was relatively okay with you warming up to her, in contrast to how he feels about Kensi. Like SNeacail said maybe you and she can at least have an extra warm friendship (with extra hugs)?
Re: your regrets about being a bad mum ... like SNeacail said we all have things we regret; Lord knows I do and I don't even have any kids. I handled poly totally the wrong way when I first started getting into it, and that's just one of my many regrets. I am glad you are getting therapy for the guilt feelings, and hope you can get some healing and self-forgiveness.
We can't turn back the clock and we can't scry into the future, so focus on the present and on being the best mum you can be in the here and now. I have a brother who's in prison and Lord knows he regrets his mistakes -- yet he has learned to transform prison life into a wondrous stage of personal growth. He is not a bad person, he just has hang-ups he needs to overcome and big mistakes that he has to pay for. I have learned that we all need a second chance. We all have our weak areas.
There's a certain excellent YouTube: Stephanie Snyder on "Learning to Live."
The overall message I got from it is: Embrace the dark, broken part/s of yourself. Don't run from it. Don't try to hide from it. Don't lie about it. Don't hide it from others. Admit that you're a screw-up, and that that's ... okay. Examine your weaknesses so as to understand yourself better as a whole person, not just as a "conveniently edited" person. Humans are both naturally good and bad inside (but ultimately good at the very core). You have to be able to embrace the bad in order to get to the good. Vision of one's worth and purpose in life lies just on the other side of the very thin line that divides vision from shame. So if you are feeling ashamed for any reason, you're probably closer to enlightenment than you realize. Don't hate yourself; just learn from yourself, and be completely honest about all of who you are.
Seems to me like you're already on the right track.