changes of sexual desire that look suspicious, unnecessarily

if a girlfriend doesn't want to try oral / anal sex with her boyfriend 

and then girlfriend reads something or talks to someone 

and then girlfriend wants to try oral / anal sex with her boyfriend, 

then boyfriend might feel betrayed because he feels that girlfriend wants to try oral / anal sex with him, 

not because she desires him, 

but because she learned something from someone else 

it would probably be the same if girlfriend didn't want to try oral / anal sex with her boyfriend 

and then boyfriend and girlfriend broke up their relationship 

and then they became together again, 

then girlfriend wanted to try oral / anal sex with her boyfriend, 

then boyfriend might feel betrayed because he feels that girlfriend wanted to try oral / anal sex with him, 

not because she desires him, 

but because she had become attracted to someone 

that's probably the psychology