Dear, good to see you here.
You definitely do not have any problems with your sexual functioning mechanism, no erectile dysfunction
, no premature ejaulation etc. Over and above you are doing very well with your loving wife.
This clears one point that love and affection are basics for sexual happiness.
With your girlfriend, love and affection is minimal or not available.
Over and above you may be guilty.
Keep cool. multiple sexual life can hamper your physical as well as mental life.
Be faithful with your wife and life, enjoy throughout.