Would you consider this situation cheating/betrayal?

Seven months ago I met my current boyfriend, Bob. He introduced me to all of his friends, including this guy named Sam. Sam had just come home from the military, he lives on a base 12 hours away. The night Sam and I met, he and I had an immediate connection, and we ended up flirting all night. We gave each other constant looks, we had amazing chemistry. So Sam and I stayed friends through MySpace (and yes, Bob knew about it). A few months later, Sam came back from the military for a short vacation, and Bob, Sam, and I all went out to party with more friends several nights. It got to the point that Sam and I were following each other around and flirting all night long. We were both relentless about it. Luckily, Bob never noticed. The last night that we went out before Sam had to go back, Bob and I got into a huge fight and broke up, and I stole Sam's number off of Bob's cell phone, and called him when we got home. I ended up going to Sam's house, where we confirmed our feelings for each other, and ended up making out (it was amazing!). Long story short, Sam and I have been keeping communication with each other behind Bob's back. I never told him that I got back with Bob eventually. Bob is very invested in our relationship, and is deeply in love with me, which makes things hard. I have deep feelings for both men. A few weeks ago I ended up getting really drunk, and I wrote Sam a letter about how much I liked him and how great he was. Since then it has gotten very sentimental between me and Sam, all the time while Bob has been trying to work on improving our relationship. The thing is that while Sam is away in the military and can't even offer me a relationship, Bob has a great job, great pay, he's madly in love with me, and wants everything to work out. It seems like an obvious choice, but Sam and I have so much more in common, and I feel more strongly for him. Bob has too many shortcomings... Last night Sam offered to pay for half my plane ticket (on his meager wage) if I would go and see him where he's stationed, and I said yes. Every time I talk to him it gets deeper, but I feel wrong because this is one of Bob's best friends, and I feel like I'm lying to both. I'm going with both because I'm not married to either one, and remain independent, but I do kind of feel like I'm cheating, even though Sam and I don't have a physical relationship. Do you think I'm wrong for what I'm doing??? How does this sound??? Am I a bad person for doing this???