Trying too hard

So the last few years have been quite the learning experience as far as life goes. When I started seeing my girlfriend she slowly introduced me to her son. We got to know each other fairly quick and became good buddies. We both have many of the same interests so it made it easy for us to bond and talk and participate in the things we had in common. We both love to go fishing, riding motorcycles, fly kites, play video games and many other things. As time goes on my girlfriend and I move in together and all of a sudden we are pretty much a family. I have been married before but did not have any kids so that pretty much sums up my parenting experience. Not that I am a parent really here but have taken a bit if this role due to the living situation. I am fine with that and am glad for the chance. My girlfriends son does have a father but he is a long-haul truck driver and pops into town on a whim. So when he is with his dad he really gets spoiled and I realize that this must stem from being away so much and he feels the need to buy him excessive things and spend a few days or weeks just playing. So that is where their relationship seems to be at. His dad calls and he gets to have nothing but fun with him all the time. So here lies a bit of my quandary. I live with him and feel I need to walk this fine line of parent/buddy. Yet I need to also be tough when the time calls for it and it is damn hard to do it right. (not that I am) I want to be a good mentor or role model for him but feel at a loss sometimes due to the relationship he has with his father. Don't mistake me for thinking he should not see his dad. A son needs a father and there is never a replacement for good ole Dad. I suppose in some ways I simply feel like a good enough replacement until his dad arrives. Then it's see ya until I need ya. I guess an example is in order. I mentioned earlier that we both like to ride motorcycles. Well he has a two stroke and as happens with them they need rebuilding and the motor must be torn down and the piston and rings replaced. I have been ordering parts and spent about $130 so far not including my time and I have not heard any sort of thank you or extension of gratitude. I even showed him the parts that I had just picked up and he looked at them and walked away without a word. Not that I want him to jump up and down thanking me or anything but I suppose a little something. So the other end of this story is that he has gotten into playing with yo-yo's. He was on the phone with his dad daily asking him to buy a yo-yo off the internet and when he finally did he anxiously checked the mail every day waiting for it to come. When it finally did you would have thought he got a new car or something. He literally called me first to tell me it had showed up. Of course I had to read into that one. I think that leaves the rest of my issue pretty obvious. I spend a lot of time with her son to teach him how to fix things, new fishing techniques, or just how to be a man. I try really hard, I really do. I just feel that the more I do the more he expects and the more he turns to his dad for comparison. I don't want to be in a competition and never intended for it to look that way. His father and I are such different people no one could ever really compare us in any way. I will just keep it in my mind that some day he will look back on these years and the ones to come with a realization that I tried. Maybe a little too hard, but I am trying.