Was the relationship toxic or just your reaction to sub drops? Actually a more salient question, were you part of any BDSM communities while you were with him? There are forums that are specifically for subs and their concerns where you could get a more targeted pool of people who understand more fully what you are experiencing. Sometimes therapists think BDSM is the problem that needs to be fixed and not the emotional fallout from using a sexual act to alter your body's chemistry, so it can be difficult to find someone that isn't going to try to fix the wrong thing. That's actually a large part of what sub drop seems to be. You put your body in a high mode where it produces mind-altering chemicals. The problem is that when you do this to yourself that you also have to deal with your body's natural fallout as it tries to regulate the chemicals back to a regular level. It's kind of like the emotional equivalent of a hangover after getting drunk. Since you said you're both married, neither one of you is really going to be in a position to be there for each other to help ease that 'hangover' feeling of sub drop. If your relationship was otherwise healthy, it's possible that you don't need to completely quit BDSM so much as develop a plan for dealing with the drop in such a way that the impact is minimized.

Try things like cuddling more with your husband after a session, and see if he is willing to offer the aftercare your Dom isn't able to be there to manage. Get online with other subs to help work through your feelings while you're experiencing a drop. Avoid sessions right around your period because that's just mixing chemicals with hormones and then everything will seem worse. (Sorry, I'm assuming you're a female here. Ignore that advice if you aren't.) Other subs might be better able to give you ideas about how to deal with a drop that you can incorporate into your aftercare system, but if that doesn't work, or the depression is lasting too long you might have to go back to therapist to get some medicine. Or maybe you can just go to therapy and let them know that you aren't comfortable taking a medicine and would just like support while you level out.
This way you have a support system so you can explore your options to continue to scene if the relationship was otherwise healthy.

Other than that, I don't think it sounds like your progress and lifestyle changes are fake without a Dom. Those were yours and you felt proud of them. I think that maintaining a natural course as an alternative to the faster-acting pharmaceutical drugs that are more readily available requires a certain level of strength. When the drop is no longer interacting with your natural depressive state I suspect that you will discover that a lot of the changes and progress you have made is still there and you will be able to pick up where you left off without having to go all the way back to a method of dealing that didn't feel right to you. Definitely keep an eye on that, though, and don't hesitate to get on medicine if you really feel like you need to.

Good luck.