With regards to breathing (it’s always a plus not to asphyxiate one’s partner…) I’ve found a reliable technique is to employ three or four “regular” insertions and then deep-throat on the fourth or fifth. Whether it’s the woman controlling the action or it’s the man (if she’s on her back with her head hanging down, to provide the right angle for mouth & throat), this regularity permits proper breathing and can allow for sustained activity. As with all things, trust is essential especially if the guy is going to ejaculate while deep in her throat: she must know with absolute certainty that he’ll withdraw after a few seconds so she can start breathing again. One of my partners, many years ago, found this particular activity so arousing that she’d often cum when she felt me ejaculate while deep in her throat; unfortunately that wasn’t exactly ideal for either of us because at that point she lost control of her body and things became, shall we say, complicated. But it did bring us closer together psychologically as well as physically.