Nikkit: your description concerns me. Is this pain in his sternum - where they cracked his chest? If so,maybe it didn't heal completely or properly? Or is it IN his chest? In either case, I'd have the cardiologist (or surgeon) check it. It's not worth messing around with or delaying to find out what's going on.
As far as depression goes - some cardiac medications can cause depression as a side-effect. Check with the prescribing doctor and see if this could be an issue and if, perhaps, the physician may consider changing to a medication with fewer side effects or, perhaps, reducing the dose.
And as far as not being able to do everything he used to do -- if your partner has a problem with healing (or perhaps a lingering infection) he won't have the energy to do all that he used to do.
Also - we have members here who've done all kinds of things - Marathon running, road racing, and other highly physical activities. They don't (or shouldn't) play football because of the risk of head impacts, but seem to do almost everything else.
But, even if he can't do all the things that he used to do, he should have many more health years ahead of him than he would have had without having the AVR. Sometimes there may be a bit of a tradeoff that isn't fully explained pre-op -- but it's a tradeoff that's well worth the cost.
Again - consult with the Cardiologist or surgeon about this. There may be a problem that can be addressed -- but only if they know about it.