Any strong and upright man will not put up with a girlfriend still playing the field.
And do you intend to have that conversation with her instead of expecting the girlfriend... to ‘absorb it out of the air through osmosis?’
If you have never said ‘I love you’, and expect her to be faithful/loyal and date only you...then you aren’t ready for a real committed relationship! And if you aren’t promising the same faithfulness...forget it!
The reason men and women have so many issues is that COMMUNICATION is missing or non existent. Never assume she knows what you want, that’s immature and childish. We are not mind readers, although our intuition is pretty good.