So, first talk to your girlfriend. The fact that you have talked to us first is worrying. I don't mean argue with her, but tell her your insecuirities and the reason you have them.

With that said she has done nothing to warrant suspicion. Yes she has stayed longer then she has initially told you, I have done that many times with my friends. Thing is she didn't have any appointment to meet with, you didn't even ask her when will she come back. If you do make plans and they get compromised because of Jyke, then you can be upset.

>she should be free to do whatever she likes. But this seems more of a date than just a meetup.

No, if she wants to be in relationship she isn't free to do whatever she likes. However this wasn't exactly a date, 2 hours of talking and drinking isn't necessarily a date. If she is contacting him constantly or spending with him similar amount of time as with you, then will be time to be concerned. The same with your plans, if you can't make proper plans to do things with her, because she is doing things with him so often, then you can be worried. Nothing of what I have mentioned is present here from what I see in your post.