unless you become a non-returner your desire for sex is not going to go away- it will merely be suppressed by these practicses which contemplate the foulness of the body. these practices are helpful as you say to overcome excessively sexual thoughts.
now the thing about the dhamma is that it is gradual practice- it is not all or nothing - which means that by the very least we should attempt not to go to another's wife- the rest is on a sliding scale- one must decide with his/her partner at what level the sex life continues. The buddha said that to have a peaceful life one's faculties must match that of the partners- so this applies as well- if one is renounced too much there will be difficulties- I often find myself in this situations and have to take 'a break' from practice for a few days. I often try to find other areas I can practice on without causing problems.
I find it helps to know that these sexual thoughts can be overcome, if not now, then in the future -the amount of suffering this thing causes is senseless