Am I right ??

If it looks like a duck, walks like a duck and quacks like a duck" it's a duck, so yes she's seeing someone else by everything you've described, but because she's refused your offer of sharing, that tells me she's probably having an affair and has no interest in being shared as such.
I'd say she has a lover in the true meaning of the word.
Yes looking like it - just she’s so fuckin slippery and want to catch her out at it be cause she so comes across as this richeous prude where I’m a fiery bastard for even suggesting a half decent sex life while she’s out getting pumped looks like and has done before a few times with other partners - I know for a fact she cheated on her last partner even though as per usual it’s deny deny deny / gaslight and turn it back round on me . The double standards and narcissism from her is off the chart