my goal in your shoes would be to just have fun. I haven't even been on a date with my H yet and we talk everyday and see each other often. I think if I asked him to go out with me lik eyou did he would probably say no (I think I actually did and he did say no, LOL!!!).
Have fun, be easygoing, cool and let him feel that the fact that he agree to go out with you doesn't necessarily mean you 'll be asking for more. That's what relaxed my H (he is TOO relaxed now). You keep it simple, keep your eyes open for steps like Lisa described and when it's time to go, don't linger. Say good night, and walk away...
Good Luck K
Forget the issue with his cousin. Stick to the fact that he made a comment indirectly about you two.