1985 BMW 318i Battery drain

[bmw318igirl]

I have a BMW 318i (1985). Replaced the battery in February so its new. Went on vacation for 2 weeks in July. Someone ran the car for me 3 days after i left, and it ran fine. 3 days later tried to run it again and car wont start. Jump started by AAA and ran the car for an hour per suggestion of AAA guy. Next day car wont start again.

A lot of people say its an alternator problem or something is draining the battery really fast. Any ideas what could be causing the problem? I know this is a little vague, but im not car savvy at all. Any advice will be greatly appreciated.

thanks!