I actually think this is rather interesting.
When the show began I suspect the writers intended for Gwen to have a bigger part. But then they introduced MJ and like what Stan Lee said, her character just outshines Gwen's and she is slowly becoming marginalized.
I PREDICT he will actually get pretty serious with Gwen in season 2, because I would bet all the whiskey in Ireland that it ends with Norman Osborn/the real GG killing Gwen Stacy (as season 1 built to Venom, that will be season 2's climax).
But on the way MJ has supplanted Gwen as the main squeeze because, simply put, MJ is a character that writes herself. And that writing is interesting. It is why despite all previous editorial board's best efforst (the Clone Saga and HORRID "reboot" in 2000), they couldn't get rid of MJ. It was why Quesada literally wrote her out of the last half of continuity (and proved he completely doesn't understand the characters in Spidey's universe. Albeit it may have been a smart business decision, time will tell).
Along the way they also have Betty Brant, a new and improved Liz Allen and Black Cat who are all getting more play than Gwen by Peter and the writers, because Gwen is the "perfect girl" for Peter. In that way they are boring once they are together, as there is little conflict.
Season 2 I imagine will be Peter realizing he loves Gwen and chasing her, getting her and then losing her. Season 3 will probably go darker and I imagine Black Cat will be more prominent there and by the end of the show (as long as it goes as far as the writers want) I bet he will still end up with MJ. Because no matter how hard some people fight it (Howard Mackie, John Bryan, Bob Haraas, JMS and of course Quesada), it always works out that way.
I find it an interesting dynamic that Stan Lee created and John Romita Sr. perfected. It is so strong, that it wrote itself. I mean when Conaway made MJ Peter's rock after Gwen's death or DeFalco turned her into his confidant, they were always intending for it to be temporary...yet it didn't happen that way. I imagine that is what is happening to an extent in this show.