Urgh, Why do I feel jealous?

Theres this guy who im sort of seeing right now, we dated a few months back and now are trying it again, but we're not technically dating right now, just "talking"...well he's at a party tonight and i dont know why but I feel so jealous that he's going to get drunk and hook up with a girl that I cant even sleep! Am I being ridiculous? I'm not usually the jealous type but for some reason tonight its consuming! We're not even dating so even if he did, it wouldn't be a betrayal, so I guess thats what I'm worried about....sorry I just need to vent! lol thanks for listening