Dating Advice - HELP!!

So there's this guy (let's call him guy A) that I met a few months back that I was kinda interested in. I told myself that if he ever asked me on a date I'd totally be down for it. We would text every once and a while (not that much though) and I see him at church. But it felt more like a friend vibe that he was giving me and he never asked me on a date so I thought okay, whatever. He's not interested in me. So I stopped talking to him unless we spoke in person. He seems like a guy who just wants to be friends with everyone. 

About 2-3 weeks ago I started talking to this other guy (let's call him guy B) and we're getting to know each other pretty well. We are both interested in each other and I'm trying to figure out wether I like him or not. We live an hour away from each other so we don't get to hang out that much, but we do text a lot. 

But this week guy A asked me on a date and I said okay because guy B and I aren't exclusive or anything and we're still in the phase of getting to know each other. I'm kind of second guessing saying yes to the date with guy A because then I feel like I'm keeping a secret from guy B and if guy B found out he might not be interested in me anymore and I may also lose his trust. The date with guy A is supposed to be tomorrow! I'm thinking that maybe I should just tell guy A, "I feel bad but I'm talking to someone else right now. It's not that I don't want to go on a date with you, because in the past I would have wanted to! But I want to see where things go with this other person I'm talking to." Or do you think it's okay that I go on a date with guy A because guy B and I aren't exclusive? I don't know!!! I'd feel bad for blowing off a guy too though because I bet it sometimes takes a lot to ask a girl on a date. If I let guy A down I don't know what to say and how to say it without making him feel bad or it being awkward.