This reinforcement, or interdependent stage, is reached only when the couple has fully accepted each other, has shared the same space for a long time, at least 20 years, and clearly love each other as friends even more than lovers. Marked by an air of resignation, little desire to diverge paths, and a deeper appreciation of the value of each partner in the union, this level has its own traumatic times, not least when the children leave home to forge their own way in the world, when grandchildren appear and each working partner retires or becomes redundant. But now personalities and individuality almost merge together and close friends increasingly regard them less as individuals and more as a team, almost as one person, with their names always mentioned together like a two-headed being!

In our relationship, even though we should have been in this stage from our silver wedding anniversary, eight years past that time we were still back in the familiarisation stage. He treated me as a much younger, immature person with the same goals and expectations as our earlier years, while I had moved on to something dramatically different. We never got to enjoy the calmness, contentment, love, mutual support, purpose and appreciation of being on our own again. We obviously had the long marriage without the accompanying benefits.

No Need to Feel Threatened
This phase should see two fully developed interdependent people with no illusions about each other, as shown in the frequent humorous asides which are often made by one partner about the other's personality and eccentricity. There is no more need to feel threatened because the two people have shared a lot over time and have stayed together through thick and thin, mainly because they want to and not because they had to cling together for fear of being alone. They are likely to be very caring of one other, respectful, kind and accommodating.

No carping, putting down or criticising, but a firm acknowledgement of the value of each person to the continuing bond, or an air of resignation of what has to be. Each partner is dealing directly with his/her own problems rather than projecting them on to, or attempting to work them out through, their spouse. Though each realises the other has limitations, each partner is more satisfied with her/himself as well as with the relationship itself, so anxieties tend to be reduced and there is noticeable trust, warmth, understanding and space between the couple.

The main strength here is congruence. Congruence in actions, thoughts, decisions and aspirations. There is a final merging of perceptions; two individuals almost speaking the same language. The dual expectation of the relationship is the same and affects the way the couple view each other. A slight majority of first marriages last until one of the partners dies, but of those marriages that last a lifetime, most are likely to be devitalised unions: relationships where deep love is absent but there is a fondness and appreciation of each other. The people co-exist, they cohabit, they have a house, raise children together, share their income and share other necessary things, but they don't share a real emotional bonding. It tends to be superficial. They share an understanding of each other without the spark of attraction which drew them together in the first place. If that spark is present, as it was in my marriage, that is rare indeed, but tremendous.

Commitment and Intimacy
There are many other strengths in long-term happy relationships which are found in vital or total marriages. A key strength is intimacy - the closeness that permeates the entire relationship and does not even require communication. Intimacy becomes second nature because the goal is of 'growing together'. The second strength is commitment - the desire to keep the marriage going, regardless. In this reinforcement phase of the relationship divorce is no longer an option. In really successful relationships, ones with high emotion, there is also high affection, a lot of hugging and embracing, holding hands and being generally tactile, as well as regular sex which is determined by individual need, not by the apparent 'norm'. A satisfying sex life holds a very strong correlation with a satisfied relationship because one does not have to seek satisfaction outside.

The six key elements we require in the reinforcement stage are all indoors: friendship, affection, love, communication, appreciation and respect (FALCAR for easy memory). However, the strengths of this stage are contentment and security. The security of knowing that someone actually cares enough to want to spend the rest of their life with you; you won't be alone in your old age; you do not have to be someone else to get their attention and you will be respected without having to impress or to try too hard. You will also be encouraged to make the most of your existence by someone who understands your expectations and aligns them with their own.

A true friend, in fact.