Keeping Depression Hidden to Keep (Admittedly Lousy) BF from Leaving

I (37F) have an admittedly superficial and narcissistic BF (40M). Read my post history if you want details, but he's clearly in this relationship because I have a good income and drive him around and he put me out on Christmas to appease his baby mama. He is, sadly, my current FP after helping me escape my abuser. He was my first BF and I got back with him. He's moody and probably bipolar and was initially also attracted to how sunny and cheerful I can be - I am a ton of fun when I am not depressed. Right now, I am hella depressed. His behavior contributes, but the larger picture is that work is being reorganized and it's stressful and my dog is sick and I had shingles that is taking a long time to bounce back from. He got mad at me for the shingles, and I can't be the fun person he likes. He claims he won't leave me, but I am no fun to be around at all right now, and this man needs constant emotional support in addition to ubering him around and watching his kids. I can't rip off the bandaid or I fear I will spiral, I need him desperately, only BPD people know how bad it is. How can I fake a bit of happy? He's known me a long time and sees through a lot of my faking it. Tips and advice on how in general to keep a lid on my overwhelming emotions and not scare others away.