I like this guy but he has a girlfriend (sort of)?

Okay, this probably sounds very complicated because it is. I have a boyfriend but I planned on dumping him soon, mostly because I'm very unhappy but also because I kind of like this friend of mine. Sadly, he has a girlfriend (well, they're not really dating but they've both liked each other for awhile and it's easier to say girlfriend, haha) that's been on vacation for a week. I feel bad for him, she told him he can't be so clingy and whenever he texts her, she never returns texts back. He even told me that she thought about going back to her ex-boyfriend! I mean, I thought it could be possible he was at least somewhat interested in me. I was really upset today and he randomly texts me with "Aaaah!" (haha XD) and I at first wanted to tell him I was upset but decided to keep it to myself. I asked him why he was in such a good mood and he said "I'm talking to you :)" it was so sweet. We sometimes text each other with "Hai babeh ;o" and it's kind of flirty but I don't know. I love how he always talks to me first and I feel like I can tell him anything... I don't feel like I'm bothering him if I text him, unlike my boyfriend. What should I do? This week I've been sort of... backing off of him, then going back, then off... a never-ending cycle. Help?