“I want an open relationship with my boyfriend”

I am a 23-year-old college student, trying my best to balance out life. I’ve been with my boyfriend a little over four years, and I love him to death. But lately, I’ve realized I want to have an open relationship. Before I was with him, I was with someone else on/off for almost four years. I would really like to explore other individuals, at least for a few months, before settling down for good.

In no way do I dislike my boyfriend, I just feel like I truly never had the time to explore different options. He, on the other hand, is highly against non-monogamous relationships. What do I do in this situation? Is this just me being selfish?