The problem I see with military service, and many career paths, is that you lose out on the ability to effectively practice this spiritual path, such as chanting, meditations, and doing yoga daily. If I was in your position and wanted to balance this, I would look into security jobs that allowed you to go home or at least to some sort of private place at the end of the day, like a policeman or security guard.
Regarding your question on relationships, this is mainly surrounding the idea that who you associate with will influence you, for better or worse. Those who are more susceptible to this (look at your 7th house to start with) will be more influenced than others. Even if you are not directly allowing their words to reach you, energy mixture can still occur and lead to changes, especially if one is having sex and/or being negligent of the activities which grow one's Satanic influence.
We cannot entirely avoid all people, including those who follow enemy religions, but we can take steps to mitigate or limit our exposure. Those who are very deep with the enemy should be outright avoided where possible. Those who are only nominal Christians are better. Furthermore, you want someone who will respect you and your beliefs, regardless of the position they come from, as even an Atheist or Pagan could flip over some other matter.