Marriage Make Up by Penny Jordan (HP 1983)

At age 20 Abbie married Sam Howard following a whirlwind romance and they lived happily ever after...for one month until she became pregnant and he told her it wasn't his kid, that he had had a vasectomy before he met her.  She had been a virgin when she met him and never even considered being unfaithful so when he alleged it might be this other man's baby, she declared the baby to be hers and hers alone and left him.  He moved back to Australia after pleading with her to reconcile and offering her an allowance in the divorce settlement, leaving Abbie to become a strong woman on her own, raising her child and eventually turning the skills she gained from her part time jobs into a successful business of her own.

Now, however, her daughter Cathy is 22 and engaged and her curiosity about her father has led to Stuart, the fiancé, putting out some feelers and Sam's reappearance.  When Abbie first runs into Sam at a local hotel restaurant she is literally in shock and traumatized by the experience, running out of the restaurant, leaving her client stunned.  Only for Cathy's sake she agrees to meet with Sam again and they soon end up in bed - but she hates him and he's only back for his daughter...right?

I loved this book - both Sam and Abbie acted stupidly when they were young causing years of heartbreak and the emotions they experience during this reconciliation process are vividly portrayed.  It's evident that they have not lost their young connection, but both have grown up and become better people, and each takes responsiblity for the problems they had.  They truly deserve their HEA.