That's a scary place for you. And a huge burden to carry worrying about whether you going to visit friends is what will cause him to self harm. Has he ever physically harmed himself in the past?
Recently my H has started this thing he does before I go to work too. He will act like I am abandoning him for work. Other times he tells me that our dog got really sad when I left (I think he was projecting onto the dog). I noticed this a couple weeks ago when I absent mindedly snapped at him that I leave at this time everyday. So I've started trying to help him plan for my leaving.
About 10 minutes before it's time for me to leave, I remind him that I have to go in 10 minutes. Sometimes I'll say something like I enjoyed our morning together. Other times I'll tell him I can't wait to see him when I get home. If I'm rushing out the door, I'll say something about being frustrated I couldn't talk with him longer. These statements let him know that he is still important to me. And it seems to be going well. Our mornings used to be terrible but they have been very pleasant lately. (I'm going to text him to share that with him right now.) You might also try to
validate his feelings. Maybe when he is calm, or during the afternoon, ask him what it feels like when you leave the house and how you can help him with that transition time.
I personally do not have a lot of experience with suicidal ideation. My H has talked about it a couple of times and my response has been to ask him if he is seriously considering hurting himself and if he has a plan. So far to date he has said no.
If he were to say yes, then I would tell him that I am worried about him and that it would be devastating if he hurt himself. Then I would say that it's important for him to get help and then proceed to call the police or ambulance. If I feel like he is using it as a manipulation I have just said, "If you are thinking of hurting yourself then I am going to call the ambulance to take you to the hospital." That statement put an end to that behavior. This may not be the best approach. Someone with more experience in this area may be able to help you better.
Remember though, the tools we have here aren't to change his behavior, but instead to change our behavior and our response to our pwBPD. In return, our pwBPD MAY change their response to us. I'd also like to encourage you to continue posting and helping others when things are going well for you. Whatever you are doing that seems to be working during those times of positive interaction could teach someone else a new approach.