Sorry if this response gets long. I feel for you. That said, if you have kids, then no, your life would not be easier with someone else. When contemplating "what if...?" you have to contemplate that future alone - you can't just magically erase your husband and insert someone else. He's still your kids' dad and has the rights and responsibilities of a lifelong relationship with them, which will be your job to facilitate. If your situation is such that you and your kids would really be better off in the worst-case scenario of divorce - whatever that looks like to you - then it's worth considering. For me, the very real and quite likely worst case divorce scenario is that I would have to sell my house, move to an apartment in another town, uproot my kids and have them change school, sleep on the couch so that my kids have bedrooms (there are 4 of them) and would only have them 50% of the time. And would be really poor, so there goes hockey and karate and all of the things they live for. In the really, really worst case, I would actually end up paying alimony to my husband for a few years because I out earn him and he wouldn't be able to support himself. So given that scenario, I'm better off with him, as are our kids.
Your husband has an illness that has gone untreated until a few weeks ago. It will take a long time to find the best treatment and see it work. Give the PTSD therapy/treatment time to work, and the treatment for his mood disorder. Please know that if his depression has any elements of bi-polar, sometimes the regular anti-depressants (SSRIs) can make things worse and he'll need a different classification of drug. Make sure that you meet his prescribing physician, that your husband signs HIPAA releases so that you can talk to his doctor, and that you attend some appointments with him on a regular basis to provide third-party feedback on how the therapy and medication are working. Keep a diary of his moods so that you have clear evidence when you have these periodic check-ins. A person with a mood disorder is a very unreliable witness to the changes in his or her own mental health. Assuming that he's also doing therapy for the PTSD, go to some appointments for that as well every now and again. Find out what the therapist thinks, how long people like him typically take to see improvement, and what you can do to support him through this process. And, seek out counseling for yourself so that you have a safe place to vent all of your frustrations, anger, doubts and fears.
Treating a mood disorder is a long process. Do not allow him to go it alone, even if he fights you on it and claims privacy needs. Of course he needs private therapy, but you need to be aware of his progress and be a part of the feedback loop between him and his doctor(s).
My husband and I have been married for over 8 years and most of them have been tough ones. He was diagnosed with depression early on and his treatment was poor - lousy therapists, wrong drugs, inconsistent effort by him, etc. It took about 5 years for him to finally be correctly diagnosed as having cyclothymia, a mild form of bi-polar depression, and to be put on a mood stabilizer instead of an anti-depressant. He's been on this class of drugs for about 18 months and it's not sunshine and roses, but things are much better. We've also been consistently doing marriage counseling with his psychopharmacologist (it helps to have someone who understands his illness) and a separate family therapist for us and the kids. It's a ton of work, and I sometimes feel like we try harder in this marriage than anyone else I know, but it is what it is. I know that if we ever get to a point where we throw in the towel before the kids are grown, that we will have literally tried everything.
Remember that he's not the enemy, his illness is. You two share that enemy and need to work together to defeat it. No less than the future of your marriage and the stability of your family is at stake. Give it time to work - you chose him, you committed your life to him, and you both deserve to hang in there until this is treated. Once he's had the chance to treat this if he's still behaving terribly, or is abusive in any way regardless of the circumstances, then you may have to consider whether or not this can work and for how long. But for now, choose to see this a the temporarily down side of things...the "for worse" and "in sickness" parts of your vows. I hope that things work out for you, and remember to get support for yourself too.