Both fire signs, both cardinal-adjacent in energy (Aries is cardinal, Leo is fixed), which means the attraction is instant and the friction shows up fast too.
The pull
Neither one apologizes for wanting attention, and that's exactly why it works at first: nobody's asking the other to shrink.
Where it gets hard
Two people who both want to lead. Leo wants to be admired, Aries wants to win. Without a shared goal, that turns into quiet competition.
What actually helps
Give each other separate spotlights. Aries needs to move fast and alone sometimes; Leo needs to be seen without having to ask.