What should I do if I'm developing feelings for someone else?

I have been with my boyfriend for almost 4 years, we are like family by now. For the most part, I enjoy our time together, and we are best friends, but sometimes I feel like he is very self-centered, and the relationship becomes a turn off for me. We broke up for a month about 6 months ago, and he has been much better since than, but I get restless when he goes on tour with his band and doesn’t call me more often.

Anyway, he went on tour with his band for a couple of weeks, and I was home alone, and during this period me and this guy who just started subletting a room in my house hung out a lot. I didn’t think anything of it, until now, when I can’t stop thinking about him and I feel really guilty about the whole situation. This is also after my boyfriend told me he is going on tour for 6 weeks in June!

So, basically, I don’t want to lose my boyfriend who I really cherish, and I don’t really know if I want to be with another person after just being with someone for so long, but if I’m developing feelings like this, I wonder if it’s normal or if I should end it or just wait it out?