My girlfriend's dad's is trying to ruin our relationship.?

Me and this girl have been dating for about two and a half months and we have been really falling for each other and we really care about each other. I've grown close with the rest of her family and they all really think I'm a nice guy and have no problem with me. Before I explain more I think you should know that I just graduated last spring and I just turned 18 and my girlfriend is a sopre in HS but she is turning 17 in December, were similar in age but we are 4 grades apart. Thats because she got held back and I got started early so really were suppose to be Junior and Senior but it didn't work out that way. So anyway her dad doesn't like me at all he hates that I'm older than her despite being close in age, he hates that I spend alot of time with her, he pretty much hates us dating. The one time that I did meet him, I was sitting in their kitchen talking with her and her mom when her dad came home drunk. He sat down and started talking to the four of us and it wasn't pretty, he pretty much bluntly said he don't want me dating his daughter. Then we went out side and he got into my face about it and it wasn't pretty, being nice I kinda just shook my head and stuff. Well he works for the union or something so he goes to these jobs for long periods of time and stays there so he isn't home for long periods of time, which is good because it allows me and my gf to enjoy ourselves without his harrasment. But he is getting home soon and appartently he still doesn't like me, and he doesn't thnk I should spend as much time with my gf, plus he don't like it when I'm at his house so spending time with my gf is out of the question. I'm worried about him ruining our relationship what should I do?