Red Flag??

I’ve been dating my boyfriend for a little over 4 months now and he has been so good to me. No red flags or anything.

However, as of late, most of our conversations consist of him venting and going on and on about how all these people do him dirty every day, whether it’s at his job, someone on the road, or someone in his life. He just gets so upset when someone does the slightest thing wrong and I’m wondering if he either just feels comfortable with me and feels like he can confide in me, or if this is a sign of some emotional instability?

Again, everything else is fine, he has a great relationship with his mom and little sister and his best friend, but I still don’t feel like I know him very well.