There's a few conflicting thoughts I get when I read this, OP.

First, I feel that your husband, for some reason, does not like the idea of you leaning on other people, other than himself, when it comes to your fears. The why is what I don't understand. I suggest talking about this situation and his reaction in therapy. It's strange that he goes from knowing and supporting you from what's happened in the past to being cold and callious towards you when he's going away.

Then, I think about how long ago this happened and how much therapy you've had since then. In no way am I saying that what happened to you wasn't a major traumatic event, but even so, I do feel that you should be a little further along in the healing & moving on part of the process. I do think that you can't just accept that you can't sleep alone at home for the rest of your life. You have a child, and when your child grows up, they need to feel safe in their home. If you don't, they won't either.

Finally, I realize that you won't be able to just move on with this over the course of a week. I think you should do what you feel is best for now. Maybe stay at your mom's on the weekend and have your friend stay over the other nights like you said, but just try to stay home alone with the baby for one night. See how that goes. If you're able, talk to your therapist in the next session about how you felt by doing this and see if they can help you with being able to stay home alone for the majority, or at least for more than one day, the next time your husband goes on his business trip.

I've also seen others point out that you probably should consider getting a different therapist. I agree, as I do think that therapist was able to help you move through the event, but they failed at helping you heal and feel safe again.

You need to feel safe in your own home, OP.

Also, when having a baby, especially from 0-6 months (and older), it is a common occurrence to have a family member help out if the SO isn't at home. I'm not sure why he feels different about that, but having help and getting more sleep will definitely help with your anxiety overall. Even if you didn't have anxiety, it is a blessing for a new mother/mother of a new baby to have some help when the SO isn't able to at times.