I can tell you this cuz my friend was like you and she did everything imaginable to achieve the Zelos scene.
Start a new game, at the Grade Shop, and select that option that lowers everyone's "affection" (or whatever it was) for Lloyd.
As you go thru the game, satisfy these conditions:
- Try to get the Z-skits with Zelos, and answer favorably to him.
- If you run into anyone else's Z-skits, be mean to them.
- Whenever Lloyd must split up the party (picking teams), pick Zelos to join him, if possible. Mix-up who also joins Lloyd, since their affection would rise too. You don't want any one character other than Zelos to benefit from this.
- When given a choice to pick costumes (Beach, Dinner Party, etc), pick Zelos, and avoid getting costumes for anyone else, if possible.
- Complete Zelo's subquests, and avoid the titles/subquests for everyone else.
By the big Flanoir scene, Zelos should be the only one with any substantial affection for Lloyd (a disturbing idea if ya ask me).