I don't know if it's a glitch, but before starting the second part it has the Comfort and Interest meter. It won't let me increase the Interest meter at all
Crush is the highest level of interest you can get until you get to Step 3. Once they're adults, it can be increased to love.
Interest levels can only be raised, never lowered. Comfort can be both lowered and raised. Before starting each step, you can adjust the meters to your preference.
No problem! It's a pretty unique mechanic for these sorts of games, and it's really cool seeing how dialogue and such changes depending on what interest/comfort combos you choose!