The answer has got to be a NO. Lions are not ‘monogamous’ to use a human term. Lions live in prides. Females in a pride tend to come into estrus at the same time. A lion in estrus is a cat on a hot tin roof. The first male to get to a female in estrus ‘takes possession of her’ (rarely there is a fight and normally when ownership is unclear). He stays close to her and herds her. He tries to prevent other males in the male coalition getting close to her. This ‘guarding behaviour’ last for one or two days before mating and up to six days after.
Towards the end of estrus they mate less often. The male’s interest fades and the female may seek additional partners. Other pride lions then mate with her. This leads to the idea that lions share lionesses around but some males don’t get the chance to mate. Young, elderly and small males are much less likely to mate and have a lower reproductive success. It is the law of the jungle as they say but lions don’t live in the jungle but in open plains.
It takes two to tango, by which I mean when one asks “do lions mate for life?” both have to be loyal to the other and as stated this is not the case.
When there is a takeover of a pride by a male coalition incoming males kill the cubs (infanticide) to force the females to become sexually receptive allowing males to mate to produce their own offspring. The average tenure length of ‘male coalitions’ over a pride is 26 months. Male coalitions run the roost over a territory and prides in that territory.
See an article on lions mating.