As a guy, there is an insane amount of pressure to "perform". I too "suffered" from not being able to cum for my partners. (Quotes around suffered, because it turned out - it was all in my head!). It frequently turned weird and akward and my previous partners would ask the same questions you are. Truth be told, yes - I have had a number of abusive partners (despite normally being the dominant one in the relationship) this has messed up my head.
In all honesty though, it comes down to this - I LOOOOVE sex. Cumming means sex is (usually) over. So I don't. sometimes I want to, but I can't. Usually a "quickie" is a 30 min session. A session is usually over an hour. I'm used to stopping because my SO has worn herself out!
Stuff that helps:
Not making it a big deal. (Then suddenly it isnt)
Talking about how great sex was afterwards (also the bits that weren't great)
Lots of hands on foreplay
Allow him to live out some of his fantasies (this may simply be holding you in a certain way)
Going on a forced break (keep the sex, ejaculation not allowed, pants stay on. No masturbation)
Bum stuff ;) (honestly)
Porn
Porn breaks (ie a break from porn, not a porn holiday!)
Not needing to cum inside my partner (even with a condom - a previous relationship turned this into a massive head fuck. When my SO and I started talking about it, she was like "I don't care if you come inside me or just, Come on me!)
I'll add other advice when I think of it!