Marlow
Check out other girls when she's not watching, but let her "catch you" a few times. She'll think you're a bit of a playa', but she won't think you're gay.
😀 Tom
No idea (and I certainly don't know you), but it could be your mannerisms, your tone/inflection, the way you carry yourself, or (less likely) the way you dress. Next time it happens, try politely apologizing (yes, even though you did nothing wrong) and try asking them.