Boyfriend won't cum

I've been dating my boyfriend for about 8 months now, and he lost his virginity to me. In the first few months of our relationship our sex was great and he'd come every time. But the past three months he hasn't and blames it on himself, saying he gets too into his head and over thinks. We've had a rough past few months with fighting and other issues, which could be a factor BUT sex is a time for us to make up and express our love so I don't understand how the negatives could affect it, especially for a guy. He's so worried about making it perfect that he ends up overthinking and ruining it. He loves sex and he's always all over me but when it comes down to coming he just can't. Any tips? I feel partially at fault and just want our old sex life back.