Playing with Fire — Mary Larkin

Susan's boyfriend of six months, Jim, is a Catholic and her parents haven't yet found out. Jim has said all along that their romance is doomed and she must understand this - but, in fact, neither can bear not to see each other. Finally, Jim realises Susan is angling for a marriage proposal and he knows he must end their relationship. Susan is distraught and ends up being comforted (too much so!) by her sister Alison's current boyfriend, Graham, resulting in a pregnancy. Susan flees to her aunt in Darlington in shame, but has to return to Belfast when her mother has a stroke and Graham is in a car accident.
Susan gives birth to a beautiful son but still refuses to tell anyone who the father is. And there are now three men in her life - Jim, who doesn't want to be the stepfather of someone else's son; Graham, who believes he is the father and who loves Susan and believes she loves him; and Donald, a man she met in Darlington...