First, do you think straight guys are fantasizing about the female Marines during combat? If not, why do you think gay men would be unable to resist thinking about you under the same circumstances. To even raise the issue says that you think being gay means you can't think about anything else but gay sex.
Second, Marines talk all the time about the girls they're dating and what they're doing to them. Talking about the guy they're dating is no different.
Third, you're equating being gay with apparent mental disturbance, and with poor hygiene.
Finally, why is being gay or lesbian something you'd have to "worry" about? You know it's not contagious, don't you?