Am I allowed to get half of his pension in the UK and USA?

My husband of 27 years (and 3 children: 2 in college, 1 as a senior, aged 17) wants a legal separation. We have houses in the UK and one in San Francisco (he is selling the two in the UK) and I want to know what my rights are please. He says I am not. I am disabled with Multiple Sclerosis (for 17 years now) and do just a little online writing. I am on disability of $310/month but have very little income. He wants legal separation rather than divorce so I can continue to get health benefits. Please advise, especially on the issues of alimony, getting half the assets and the pension issues (he says I can have half of his $401,000 but no pension, here or in the UK).