I find that the terms attachment and non-attachment can get confusing, particularly if you're not careful to define what the object of attachment is.
How I frame it for myself is that being attached to a person is fine for me, in fact it's what I want: to feel connected, bonded at some level. It's hard to imagine having a meaningful relationship without feeling attached.
What I try to lose attachment to is outcomes. I love a person, but can't control what'll happen. Feelings will evolve on both sides, events in lives will happen, and we will just have to adapt.
Some may need to relinquish to a higher power to get to this state; for me, that isn't necessary or helpful.
I liked Tara Brach's Radical Acceptance for outlining some of these ideas. She does add in the "higher power" component, but I just skim over that, and take the bits that work for me.