It is very, VERY important that you establish your own identity as being separate from the character you play. You inevitably spend a great deal of time around your Straight Co-Star pretending to be someone you're not, and it's essential that he becomes emotionally attached to you and not your character. Frequent reminders about your identity are recommended. This can be established with out-of-character pictures and flash cards.
Justin
NOT Justin
Justin
NOT Justin
Failing this, you could burn every picture you find of your character, consistently dress in black and scream about the absurdity of the universe, but it's likely your Straight Co-Star will simply suggest therapy.