Is it normal that despite being in a relationship, i like other girls?

So pretty much the title explains it all. I have been in a relationship with the sweetest girl for about 3 months now. We haven't been on many dates. We mainly talk through things like social media and over the phone. She really loves me, however, I am questioning whether I love her as much as she loves me. Every time I go somewhere with my friend, he's followed by a few girls who obviously like him. These girls were once friends of mine whom I thought would be all to me. Now, they seem to have whored themselves out for my friend. Sorry for the language but it's true. I become infuriatingly jealous when I see these girls and my friend. My friend also constantly complains to me about his hard social life, which he doesn't have, socially speaking. Is this normal?