> I can guarantee, that trying to make someone else happy, will never ever fail to make you happy :
I can guarantee that there exist several data points that refute this.
Definitely can guarantee many cases where doing this to excess for some people is a net negative.
Can certainly show cases which led to divorce (i.e. always trying to make spouse happy was unstable, and the marriage would have been much better off with randomly ignoring spouse).
Helping others can make you happy. Just don't do it at the expense of self care.