So you aren't sure if you can trust yourself, because you feel you may be headed toward mania?
Let's say I like candy. My favorite candy store is nearby my home. Sometimes I get out-of-control and binge on candy and it makes me sick (and I gain weight).
Let's say I've had good control about candy for awhile; however, I am feeling like I am not in the best place for good control, I feel a lack of control. I feel I might binge.
Should I go into the candy store? (No for now. Maybe yes another time.)
Only you will protect you. If you are feeling you are likely becoming manic, and you wonder if you can trust yourself, then take a pass or postpone until you feel more stable.
You write you might lose him if you postpone. Wow.

How much does he really want to get to know you if he'll give up that easily?
You say he's older than you. I've been assuming you're of legal age. I hope you are of legal age. (For online fetish sites, that is.)
Remember: You are the one person most invested in your own welfare. Relative strangers cannot possibly be as invested in your welfare.
Protect your own welfare. You deserve it.

WC