Poppy--You are looking at this very narrowly, from the perspective of a young person, living in the 21st Century England. The Church, however, is very very old and spans those centuries when a woman did indeed need a man to take care of herself and her children. Even today, data for the past 100 years have shown us that single parent families are not the very best situation for children. It is true that many children who have grown in such circumstances have turned out fine; just as it is true that many children who grew up in two-parent families have turned out badly. Nonetheless, I am talking about the outcome for the majority of one-parent children
Since nobody has brought it up, Father John Meyendorff had written what I think is the definitive book on what marriage means in the Orthodox Church: Marriage, an Orthodox Perspective (St Vladimir's Press). This book is available on Amazon, as is Saint John Chrysostom's On Marriage and Family Life (St Vladimirs's Press), Preserve Them, O Lord: A Guide for Orthodox Couples in Developing Marital Unity [Conciliar Press] by John MacK, and Love, Sexuality and the Sacrament of Marriage (Holy Cross Orthodox Press) by Father John Chryssavgis.
As I recall from Father Meyendorff's book we are married not merely for life but for all eternity. The reason why the Church exercises economy and allows remarriage is more complex but it is not a theological matter, it is a pastoral one, a very human and loving response to members who need a helping hand. As Irish Hermit observed, the Church does not encourage divorce and remarriage but tries to make the best of a tragic situation. The folks who have divorced will still have to answer to the Lord why their marriage had failed and they have to make amends and atone for their part in the tragedy.
BTW, Irish Hermit is not a mere bloke or a "babe" but Father Ambrose, a wonderful Orthodox priest who is serving the faithful I believe in New Zealand.