No one ever does anything for truly selfless reasons; so-called selfless actions receive some kind of positive reinforcement. Yes, when I'm nice to my spouse, they're more likely to want to be nice to me. When I donate money anonymously to a good cause, I feel good because brain chemicals are telling me that I'm a good person. If you removed that positive feedback loop, then people would quickly start acting solely in selfish ways.
Absolutely. If we didn't have this feedback loop in our brains, humanity as a species would die out in a generation. Psychopathy is super-bad for species survival.
I was spending a bunch of money getting some items framed for myself and my partner brought me over to admire a painting on the wall. I decided to inquire about the price quietly when she wasn't nearby. I surprised her with it and she loved it as a gift. But it was also a way to feel better about how much I was spending on myself. Doesn't make the gift make her any less happy.