Well, remember, Lonelyhearts doesn't cause people to be in love like HunkaHunka. Lonelyhearts is designed to make you obsessed with finding your soulmate. So both Lilo and Zeke would manifest that in different ways, and to be honest, I think it would be a step away from romance between the two of them.
It would be like one of those comedic, wacky episodes. I'll explain!
If Lilo got hit by Lonelyhearts' breath (though that wouldn't happen because like I've said multiple times, the Experiments whose One True Place is on Kauai hardly ever, ever come to Honolulu where Lilo goes to school), she would be prioritizing finding a boyfriend - weighing options, making a big conspiracy chart/scrapbook with all the male students' pictures and hobbies on it, sacrificing turkey sandwiches and Valentine cards to Laka on the weekends, just being Lilo about it. The CHGH would be all about helping Lilo find her man (except Victoria, who would be all about curing Lilo once she realized it was an Experiment doing this, and she'd get the gang to help.) Zeke would be super frustrated during all this, unaware it was the work of one of Stitch's cousins, and have no idea why Lilo was suddenly boy-crazy and why, heaven help him, if she's suddenly boy-crazy, why isn't she boy-crazy about him? He's right there! But at the time, they're just friends, and Lilo's brain doesn't consider him an option in her fakey-love state.
If Zeke got hit by Lonelyhearts' breath, it would be a much similar situation, except Lilo wouldn't be jealous or frustrated. She'd know exactly why Zeke was behaving oddly, and she'd know exactly what to do to fix it. Shenanigans would ensue with the group, obviously, but in the end it'd be a much faster antidote process because Lilo, the reigning expert on the Experiments (aside from Jumba), is leading the crew in this scenario.
Love this!