I've always told myself this "trust your instints"! If you have suspicions or doubt its becuz he has done something to give you those feelings. If the relationship was solid, you would not be worrying.
Also remember this, as bad as this may sound, men only want one thing. Sex. And if they can't get it w/ more than one chic they will! If anything you should be using him as a booty call!
It's only been a month and a half for you in this relationship, maybe you should take a step back and enjoy the relationship for what it is now. Don't rush into anything serious with this guy. And for god sake I hope condoms are being used, especially if you have suspicions! Always better be safe then sorry!
There are plenty of men out there, don't get yourself wrapped up with a guy whos going to make you feel this way....its just isn't worth and and life is toooooo short!