what are the customs or halachas in reference to a widower who remarries,in reference to the first wife, how does he or does he observe the yartzeit, does he go to the cemetary, etc.
Pnei Baruch (39:19) writes that a widower should not observe the yartzeit of his first wife in the presence of his second wife. This would include any overt acts of commemoration. This is based on the Gemara (Moed Katan 19)that writes that people should not console a person who remarries for his first wife. However, other authorities differentiate between consolation and commemoration (Seridei Eish, 2:136; see Nahamu Ami p. 96 who writes the point specifically concerning lighting candles). Yet, Be’er Moshe (4:194) writes that one should not commemorate the yahrtzeit of a first wife, and Kol Bo (p. 404) writes that candles should not be lit for a first wife.
It thus emerges that there are many opinions who uphold both sides of the debate. If the commemoration of your first wife is important (I imagine it is), then you could perhaps perform those commemorations that your second wife will not note. If she is happy for you to commemorate your 1st wife, then you could perhaps go further an light candles, etc., but it is hard to know a person’s heart.