Boys maturing slow

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I just broke up with my boyfriend of 3 years bc he just doesn’t know how to be in a relationship with someone. As far as treating them right and acting like a man. We’re both 21. I’ll be graduating college in May and I’m already apart of “adulthood”. He’s kinda childish and selfish too. And literally everyone (WOMEN!!) keeps telling me boys mature slower than women, you have to teach them this and that, just work with them blah blah blah! I’ve been trying for 3 years now and yes he’s gotten better on some things but it’s exhausting at this point. Especially when I have so much going on in my own life and mind rn. It just drives me crazy that women keep making the same excuses for boys and men so the cycle will never end!!