My bf and I have been together for 7 mos now. At the beginning he would last for like 30+ and he can get hard again after a few minutes and last even longer. Nowadays, he'd last for 2-5 minutes. Is the problem with me or is it him? Am I no longer good enough for him? 

If it matters, I'm 22/korean-filipino/5'1/ average body and he's 25/arabic-american-french/5'8/a bit overweight.