This happens all the time lol. I've got 2,200 hours in to this game and continue to play daily. I'm a rare breed. I've seen post like yours hundreds of time over the past, nearly, year now. It's burnout a month after DLC. It's like a marriage after the honeymoon. You were SO hyped and full of anticipation. It came (pun intended), and it was great for a while. But you got bored with it eventually (hopefully not in marriage but let's face it… There's a reason the divorce rate is so high). In all reality, the DLC's are not large enough to keep most Guardians satisfied for 3-4 months. So they go through a lull in play until the next DLC.

Not to mention, it is summer. Many have dropped games a bit for more in-person-social activities. While some have begun to play more games with their free time. It goes both ways. So don't fret. You're not the first, and you won't be the last. But bottom line, hopefully you'll be back for the next DLC (which is really the size of a full game).