There is a fair amount out there on the web about spousal support and retirement. My colleagues discuss the leading cases quite intelligently. I recommend that you read what they have to say. I am going to distill down the current wisdom based on the cases to a few numbered points. But remember, each case is different. Before you plan to retire, it pays to have a consultation with a family law lawyer.
I don't like Separation Agreements. Many would surely disagree. In my view, Separation Agreements are not always that easy to enforce. It is much better to have a court order, especially if you seek to enforce a parenting plan. While the provincial government has a government agency mandated to enforce support orders, no similar agency exists with respect to enforcing parenting provisions. So, I don't like Separation Agreements.
It is a challenge at the best of times to achieve a legally enforceable spousal support separation agreement with a former partner/spouse. Is it legally possible to achieve an enforceable "air tight deal" when the former partner/spouse is mentally ill? We say: "unfortunately - no".