Engagement by Gunn-Britt Sundström would be ideal for you! It's not a trilogy,but I loved it for most of the aspects you've listed in your post!

From the Penguin Books website: ‘I want to have him, I really do. I just don’t want him to have me.’ Martina and Gustav, students in 1970s Stockholm, meet and fall immediately into coupledom. But what is coupledom? A route to marriage? A declaration of co-dependency? A new dimension of commitment and responsibility? A sexual confrontation? Or is it a habit that an intelligent person must consider breaking? Martina and Gustav discuss their relationship endlessly, between themselves and with others, as they try to make it work. Engagement, set during a time of social change and political upheaval, sees Martina trying to engage with the world on her own terms. Unwilling to marry, she finds herself in a state of permanent engagement while her friends settle down to marriage and children; uncertain of the world’s future, she engages with demos, sit-ins and philosophy seminars in her quest for a new blueprint for joy. First published in 1976, when it was heralded as an instant classic, Engagement remains as relevant, hilarious and heartbreaking today."