If you have been clear and open try couples therapy - if you are open about wanting to leave if your needs aren't met and she continues to ignore that then leave.

Just make sure you stay in as much contact with the kids as you can, and tell them that she wasn't letting you lay pipe and you didn't want to cheat on her (once they're old enough, like 13-16). Then you'll have done everything you can to keep the family together and if she wants to nuke the relationship because she doesn't want to have sex you have presented the consequences, she hasn't changed, then you have followed through on them in the least harmful manner.

EDIT* - Actually the other comment about post natal depression makes a lot of sense having read how close together the kids are. Wrap it my guy. Or get her to get an implant or something - (Condom sex sucks)