If you listen to the dialogues between her and Jowan (and you can actually speak to Jowan after they join you) you hear the silly, optimistic and totally stupid dreams they have about him giving up magic and them going to live on a farm. They just sound like every other very young, naive kid in love I've ever witnessed.
Jowan can no more give up his fascination with magic than she can actually accept his magical nature. Burying your head in the sand and pretending it will go away isn't very effective, but that's what they plan on doing.
I agree, they do come across as naive teenagers who're so sure their love will conquer all, but the moment their resolve is tested they fall apart.
I wouldn't say Jowan tampered with blood magic out of "fascination with magic," though. He comes across as pretty whiny and pathetic when you meet him, and if you pick certain dialogue choices he reveals that he was never an especially gifted mage, and always envied the PC for being so gifted. Add this to how his Harrowing was long delayed (he came to the Circle a year before you, and is implied to be older than you, yet you got your Harrowing first), and how exposition reveals that mages who are considered too weak for the Harrowing are given a "choice" between death and Tranquility instead, and it's likely that Jowan got scared that he'd be considered too weak for the Harrowing and desperately tried to "cheat" by using blood magic to come across as a stronger mage so he'd get his Harrowing and not the chopping block.
At least, that's how I interpret it. I don't personally interpret Jowan's tampering with blood magic as "fascination with magic," I interpret it to be a desperate attempt by a weak idiot to avoid the "death or lobotomy" ultimatum presented b a failed system. They force all mages into a tower, then constantly watch them to make sure they get neither too strong nor too weak. However, they punish the weaklings with death or lobotomy, so of course the weaklings get scared and resort to corruption (in Jowan's case, blood magic to make his spells stronger) to make themselves stronger to try to avoid getting killed or lobotomized by their jailers.
THAT SAID, I do think Jowan's and Lily's belief that their love is strong enough to face all odds and all their problems will be solved by running away to a farm is painfully naive and stupid. It certainly doesn't help that they're quickly spotted right after their "foolproof" plan was put into motion, and Lily quickly turns on Jowan the second her love is tested. "Oh, we're so in love, we're so in love, nothing can come between us, our love will conquer all--OMG YOU'RE A BLOOD MAGE?! GET BACK, MALEFICAR!"
So much for true love. 
I think they might've been fine, if not for the blood magic. Nothing wrong with her silly dreams imo. Abominations are so overrated
Especially if they went out to a farm or something. I doubt it'd be as stressful as Kirkwall.
But that's probably a whole other can of worms. The idea of stress and magic. I think that's the main culprit that causes even worse problems. Take out the stress, take out the problems.
That's the problem though. Life is stress. If they can't deal with small challenges, how are they going to deal with big ones?
Let's just say their plan worked and they did manage to get away. They have a whole new set of stresses to worry about. Since they're a mage and a Chantry sister on the run, they'll spend the rest of their lives looking over their shoulder, worried that they'll be recognized by local Chantry officials. And since they're penniless and farming is backbreaking labor that pays next to squat, they'll be doing hard labor for years just to put food on the table.
Not to mention, farming is difficult and unpredictable. It's not like Farmville where you just stick seeds in the ground and they instantly grow. Sometimes they don't grow. Sometimes they grow too slowly or not well enough. Sometimes they get stolen by people or eaten by wild animals. Sometimes the weather's against you, which could mean life-or-death in the middle ages back before irrigation. Since the food they grow is the source of their income, every drought, every flood, every frost, every blight (lower-case blight, like mold or rot, not upper-case Blight like darkspawn) could mean the difference between putting food on the table and going hungry all winter. Not to mention how backbreaking the labor is by itself if the crops grow as planned.
I wonder how much Lily would love Jowan when she has hard hands from hard labor, weak from child-bearing, living in a little hut, worried about whether the local Chantry in the local village will ever have people who'll recognize them, worried about whether or not this year's crops will grow enough to make rent, pay taxes, and have enough leftover that they'll have enough to eat during winter.
I think it certainly helps that for all her, "Oh, we're in love! Nothing will ever come between us, our love will conquer all!" the second Lily's conviction for Jowan was tested, by learning he was a blood mage, she instantly turned on him. It wasn't even just, "Jowan, you lied to me," or "I never thought you were the kind who could use blood magic," he was a completely different person to her. She instantly demonized him, and saw him not as a man who made a dumb mistake, but a monster wearing a man's skin who lied and used her from the very start.
Honestly, if Lily's love for Jowan could evaporate so quickly and easily over such a small thing, she didn't love him as much as she thought she did, and something would have come between them sooner or later.
My latest Amell Louisa did as well.
Our Amell's are the supicous sort, aren't they?
I feel like the lone Surana in a sea of Amells. 