You can be in love with two people. However, it can be challenging since you will have divided attention and commitment as it is hard to serve two masters at the same time. One needs to find out who they truly love and stay committed to them to make the relationship work.
I'd say yes and no. For me, loving someone in a romantic way means that they are you're one and only, the only person you would even wan't to be with, but for others that may be different. To each their own.