Tough situation amongst friends...?

I'm having a difficult situation with two of my friends. It's hard for me to summarize above. I am a 25 year old straight male, who has 2 younger friends, (20 and 22), both male also, who have been putting me in a difficult place in our friendship. The 20 year old (let's call him Bob to make it easy) and I have been friends for 2 years, and though our friendship has had it's ups and downs, we have managed to maintain a strong friendship. Throughout the course of the friendship, Bob had demonstrated some attachment and obsessive issues. There were a few occasions when I didn't answer my cell phone, and I was busy, and he showed up at my house. Also, time where he was angry with me because he felt as if he wasn't getting the attention in our friendship he deserved. We talked about all of this, and I thought it was resolved. Though he has never said anything, I do notice that he looks at guys, and I suspect he may be gay. He is the product of a single mother home, and refuses to share much of he past, before moving to our small town 2 years ago. I don't have any problems with gay people, and I would still be his friend no matter what his sexual preference. Then, a few months ago, I met another friend, who we'll call Steve. Steve and I have a lot of similar interests, so we ended up becoming really good friends. We both are straight, and enjoy musical theatre, and will talk at length about some of our favorite shows, and other topics. Because we are both talkers, and Bob isn't, I believe he often feels left out, but when I try to include him, he shows no interest in the topics we are talking about, and when I pry for a subject he's interested in, he doesn't want to share. This problem has started to come to the point where Bob is becoming angry, and has yelled at me and Steve on several occasions, and insulting us. Bob always apologizes for his behavior, but it still makes me a little uneasy. I've also noticed that Bob stares at me a lot, and will often avoid talking to me in group settings. I chalk much of it up to immaturity, but I would think someone who is an older 20 would have some of these problems under control. I'm very confused as to what is going on, and how to address it. Does anyone have any input? Thanks!