Rose22, I'm an old guy (•https://mydramalist.com/profile/lesle), here's how I see it:
The love Park Dong-hoon develops for Lee Ji-an is pure Human Love. Not physical, not sexual, not romantic, but simply the caring love of one human for another. Why? Basically, because that's just the kind of guy he is.
Lee Ji-an has her shields up full, in the drama the only person she previously let into her life was Lee Kwang Il (Loan Shark), whose father she killed. That's a deeply convoluted, complex relationship, but at the same time one she holds onto as part of her shield from life.
Toward the end of the drama Ji-an, because of Dong-hoon it seems to me, begins ever-so-slightly to emerge from behind her shield.
Open Ending: Well, anything is possible. As other comments have pointed out, Dong-hoon's marriage is over, he and Ji-an are back in the same city, they know where each other are.
Recall that toward the end of the last episode, in the cafe, amid the hubbub she hears his voice from afar and just turns and walks toward the voice.
And in the conversation they have Dong-hoon says to her about his new workplace, "come by sometime." And a bit later on Ji-an says, "I'll buy you a meal...I want to buy you something delicious, Mister." And then Ji-an says, "I'll call you."
They walk away from each other and have this inner monologue: He "Ji-an. Were you able to find some comfort for yourself? She "Yes." "Yes."
The Handshake: No deep symbolic meaning. Just two people glad to see each other, physically connecting, touching, holding on to each other, in an acceptable manner for the circumstances.
It's the words they say to each other that count!
It's an open ending fraught with possibilities and it's up to us to decide what we would like to happen. Myself, in a few years when Ji-an's a little older, yes I would like to see them get together. But that's a story for another day. You, others, may feel differently.
I very much recommend watching this kdrama more than once.
Rose22, welcome to MDL & stay safe out there!