Guy situation - Help!

So I started this new job about a month ago, was really crushing on someone who worked in a different area of the workplace.. he'd make us all cups of tea and started giving me the cups that said "I love you" and "mine" on.. didn't think much of it. Then he put a sticky note on my computer saying "smile".. started buying me cookies, sweets and putting them on my desk, making me cups of tea and putting them there ready for when I got in. All the little things was incredibly sweet.. started talking to him and he's really nice and respectful.. although my ex works with him and everyone else at the workplace would go nuts if they knew we were speaking. I've seen him a few times, haven't had "sex" but kisses, cuddled and had some really deep chats. He's not really the best looking guy but his character is great.
Then this other guy, who I'd had a crush on since school, started messaging me. We'd messaged on and off the past year, not much just casual talk not getting anywhere. I personally think he is way out of my league. Last week we were messaging and I thought, sod it, so I asked him to come to the pub on Saturday night as there was a party on. As soon as I saw him I was struck for words because I'd forgotten quite how good looking he is. By the end of the night we were talking, he was stuck by my side and had a really nice deep chat before he got a taxi home. He's messages me tonight.. started flirting, adding more kisses on the ends of each message etc.. I'm squeeling with excitement thinking.. one of the guys I've always liked is messaging me, really likes me for who I am, is a genuine nice guy and is way out of my league. I still can't believe he's talking to me! We're getting on really well.. 
Out of the two guys, they're both older than me. The one I work with is 29 and the other one is 25. Out of both situations, the best one to go with would be the guy I don't work with. However the one I do work with has started getting feelings for me and I feel like I'm really stuck.
I need some advice on how to let the guy I work with go, without telling him bluntly I guess.. so we can still have a laugh at work and be friends. I don't want him getting hurt before it gets too deep.. help!