Where is the line between occasional drinking and being alcoholic?

Well, I guess you are already aware of the possible complications that might occur here. And I suppose that the test is quite simple. The next time you feel the urge to take alcohol, try not to take it. If you succeed without any problem, than I guess you are ok. But if you fail, then there might be something here to think about. Still, I think that you sound reasonable enough to quit on time.

My neighbor is a weekend drinker only. He drinks from Friday nite after work to Sunday around noon. He controls his urge during the week.
I know of others who have a drink or two every day, 7 days a week.
And there are those who drink from sun up to sun down, daily. I guess if you have the ability and strenth to control your drinking, you are not an alocoholic.
If you are finding it difficult to supress your urge to take a drink, maybe you could look in to AA meetings. You are obviously concerned and fear that this may turn into a problem for you. That's good that you can see that a problem may be on the horizon.
You do not have to be an alcoholic to go to these meetings.

I am a 59 year old man.   I have done my share of 'loosening up' in my lifetime.   Take a good look at just what 'loosening up' means.  Some have 1-2 drinks, others buy a 'case' or a' bottle' for the week-end.   Your amount to do so will increase over the years, t is your tolerance level.  Watch out for that as it increases.   Ask those around you who you care about what they see and what they think.  It is far better to have open discussion now, that full blown arguments later.  Any best friends that you drink with will not have a balanced, honest opinion as they most likely enjoy your progression regardless. 

Adjust or reinvent hobbies or pastimes to circumvent the drinking activity.  Eventually, these will replace the loosening up behavior. 

By the way, I have been through treatment, the hard way, after a lifetime of drinking with  best friends, college buddies, business colleagues,  and family.   Eventually, it exhausted me.  Now, I really don't care if I have a drink or not, certainly, not to loosen up.