Leigh,
So sorry to hear your devastating news, and sorry too not to have replied earlier to your post. (This board can go vey quiet and then the days you don't check it...).
You are not to blame, absolutely not, for your loss.

I've just been on another board and somebody there has posted about relationship difficulties after losing a baby: it is so, so common. Men and women also grieve differently. They do not express things in the same way, men tend to focus on the future rather than analysing the past, and it's important to say it's not about one being better than the other, just different, and this can cuase tension.
You have two issues: grieving for the loss of your children and a relationship that was already experiencing difficulties. Hard as it might be to take the plunge, I would recommend approaching Relate, the relationship guidance people. My Dh and I went for a while, and I was very disappointed to find that, where we are at least, there are not relationship counsellors trained in helping people who have lost a child. Interestingly, somebody on OFB had found a counsellor via the local children's hospice, which makes perfect sense. Getting back to Relate, they are a charity and will get you to pay if they can, but I don't think they will push it.
Talking to people does help, so if you have supportive friends do take up any offers to talk or get out, and I personally think having a third party help you talk about your relationship is worthwhile.
Gilly
Sorry too to hear you are suffering with MS.