Regarding the other sons, the Torah gives the reason before the name. Why is Reuven different?
Moshav Zekenim: His name is put first to praise him (like Rashi brings) - see the difference between my son, whose Bechorah will be taken and he is silent, 1 and Esav, who wanted to kill Yakov for taking his Bechorah (Berachos 7b). 2
Divrei Eliyahu, Kol Eliyahu, Ha'Emek Davar: R. Eliezer expounded so. Why does he expound unlike the Torah's reason?! Regarding all the others, it gives the reason before the name. For Reuven, it says the name first. This shows that there was a reason to call him Reuven other than the reason written.
What is "b'Onyi"?
Tosfos ha'Shalem (5, citing R. Efrayim): (It is withholding Onah, intimacy at the proper times.) Yakov does not even fulfill [with me] the Onah of a Chacham (Shabbos night). 1
Perhaps she could accept that Yakov prefers Rachel, but even when Rachel was Nidah, Yakov would not fulfill Onas Chacham with Leah. (PF)